I have all the expansion packs for Sims 3 currently, but some of them were purchased and downloaded from Origin while the others I downloaded from the expansion disks. If EA shuts down Origin some day and drops support for Sims 3 completely, would I still be able to play with the expansions I purchased off Origin? Or what could happen entirely?

Also, would store content be safe if already downloaded before the store could get shut down?

Not sure if either of these will happen in the near future, but I would want to be prepared and know what may still work or not.

Your store content will be fine even if the store isn't there. Reinstalling it on a new computer or a new user game folder would be impossible unless you already had your content downloaded and safely backed up/put away elsewhere as you said to bring out again for the Launcher to read and reinstall.

We don't know what will happen if/when Origin goes away or if it were to stop allowing TS3 logins. We imagine a way to play the game offline would be provided -- that's already in place for Patch 1.69 players but it's kind of goofy as you have to specify offline play while still online and you end up online again if an Internet connection (to Origin) is detected. Hopefully that will be improved upon. The entire point of Patch 1.67 (over 1.66) five years ago was to allow for an eventual graceful shutdown of EA's TS3 servers.

What we don't know is how one would install or re-install a game or pack that was digital-only should the need arise if Origin isn't going to serve up the digital installers any longer. That seems unlikely to happen, though. Although they no longer offer the TS2 Ultimate Collection for example to players who do not have it now, it's still an Origin product and available to those who already own it and need to re-install.

Some comfort should be taken in the fact that EA is still selling the game. They can't pull the plug on it even if they were to stop selling it tomorrow as players purchasing it today expect it to continue running as is for many years. We've also seen that EA shut down the servers for the console versions of TS3 last year. TS3 still runs for those who have it on consoles, just without the online elements, so perhaps some comfort should be taken in that as well.

That's really great to know! It was a worry of mine for a little so this helps put it at ease for me. Thanks!

that's a valid concern, was mine as well, so I'd like to add my little two cents on this...
(just for the sake of the conversation, no other reasons, or to defend EA)

me too I've started TS3 and soon after the first expansion pack Ambitions, from a hard copy on a CD-DVD purchased on a store, Best Buy if I'm not wrong, then slowly I've transitioned to the digital copies using the EA's portal Origin, now with me installing the full game packages TS3 and expansion packs only via Origin, since I don't even remember where I have stored the old CD-DVD's to stat with...

I for one, I was particularly concerned after the big fiasco in 2015 when EA and closed down, totally shut down the servers of NFS Word, that was the online racing game adaptation of NFS series, very successful among car racing fans, with over 2 Mil. users worldwide, of those, at least 5% of premium membership users - aka paid membership privileges - myself included being one of those with a paid membership...

they, EA, just decided after almost 3 years in existence (was launched sometimes around 2012) they decided the project is not feasible anymore, servers won't worth the maintenance costs anymore, developers won't worth the maintenance expenses anymore and such similar reasons and just shut down the entire project in August 2015 after giving the users a 30 days in advance warning and plenty of free bonuses to enjoy for the last 30 days, as a way to compensate for the inconvenience...

despite the free bonuses and the polite apologies, it was a huge fiasco, since many, many users spent thousands of US dollars in acquiring what's known in the industry as "virtual assets" - digital items a player/user owns in a virtual environment, like an online gaming platform - many spent tons and tons of real money (myself included) to acquire a great to awesome collection of racing premium cars, to own and use during the gameplay, only for the game to close in 30 days... not many took that so lightly, so it was a bad, if not ugly mark on EA's portfolio, still is and always will be...

at that time, me too I started to wonder, OK, what if something like that will happen with Origin, what will happen with my TS3 game and expansions..??..

so, it is a valid and reasonable concern and in the non-perfect world we live in, it can and it may as well happen with Origin too, anytime if "the powers that be" at EA will decide that...

back then, in 2015, I've even contacted Origin support regarding this concern, like a ripple effect from NFS World shutting down, since some users on NFS World were speculating during those last 30 days as if that will close - NFS World project - then major issues are happening internally at EA, so Origin may close as well soon after...

so, back then, I've contacted Origin support, via online chat, ending up with a nice and polite CSR someplace in India or in that region that at their level, assured me with some confidence that Origin won't shut down anytime soon - we're in 2019 now, and it doesn't seem to be any risk of Origin shutting down, especially considering Origin is a sales portal, a revenue source securing what can be assessed as more than just a steady stream of revenue for EA, since all the games published under EA label are now sold via Origin portal, is their online store, so chances are slim to none for Origin to close anytime soon... it may be slow at times, due to maintenance issues, but I personally don't foresee closing Origin anytime soon...

on top of it, just my own personal opinion, I'd like to think that EA as a corporation, as a publishing company and Maxis operating under EA umbrella, are still respectable and reputable companies, with a reputation to preserve, even to improve, especially with the fiasco of NFS World, that many remember and are aware of, over 2 Mil. active users worldwide, is not to ignore, and they know that...

maybe some of you guys reading this already know the story and as such you know what I'm talking about... if you directly were not involved with NFS World, then consider yourself lucky for the fact you were oblivious of how much damage EA inflicted to the users involved with that project...

to conclude however, I do think in the worse case scenario if and when Origin closing may be looming, I am almost sure they - EA and Maxis - will allow the existing users, us, the ones using now Origin, to somehow save our games packages for later use, even to send us via mail, a hard copy on a CD-DVD whatever the case may be, on a case by case basis... I'm sure they'll find a way to accommodate the customers, us, the users of today's Origin

nonetheless, this is a valid concern and I'm somewhat glad to see I wasn't the only one worrying about this at one point in time - my Sims, are like me, with the "neurotic" trait included... hehe...