Am I able to play a free game on a PS Plus account that was downloaded from an ex-PS Plus account

You will not be able to re-download them, or play any games that you had previously downloaded & installed via Playstation Plus. If you try to download any of the games from your download history, it will not work.

However, if you later decide to renew your subscription, these games will become available for use again. They are even re-downloadable, as long as you added the games to your cart and successfully checked out before their free offer period passed.

Q: How long do I get to keep the free games with PS Plus?

A: Games you get with PS Plus are free to download with a PS Plus membership. As long as you are a PS Plus member, you’ll always have access to any game you’ve added to your library, even if you’ve previously deleted a game from your hard drive.

Q: If a game is no longer available for free with PS Plus, can I still download it for free with my PS Plus membership?

A: If you did not add a game to your library when it was free with PS Plus, you will not be able to secure your free download. However, if you added a game to your library when it was available for free, but it’s no longer on your hard drive, you can visit the PlayStation Store and re-download it anytime, as long as you’re a PS Plus member.

Q: How many times can I download / re-download a game in the Instant Game Collection?

A: Download a game as many times as you like, even if it’s been deleted from your PS4 hard drive, as long as you’re a PS Plus member.

Q: What happens to the games and add-ons I download for free through a PS Plus membership if I decide to not renew my membership?

A: If you do not renew your PS Plus membership, you won't have access to previous free games downloaded with PS Plus. If you have purchased add-ons for a game you received free with PS Plus, and the add-ons require the free game to play, you will not be able to access the add-ons if you choose not to renew your membership.

Should you decide to re-activate your membership, you can again play all free games downloaded, along with all purchased add-ons for these games. Alternatively, you may also purchase the specific game to access any purchased add-ons for the game.

More information can be found at PSN's Support page here.

You'll still have access to the games you've downloaded, even if they're removed from the collection or you've deleted them off your system, as long as you're still a subscriber.

If your subscription ends, you won't be able to access those games, but they'll still be available again if/when you resubscribe.