Technically, yes, if you’ve previously purchased them on Steam, they remain accessible. However, this might not apply to multiplayer games, or those which require authentication, as they rely on external servers, which might no longer be functioning. This article gives more insight into this matter.

There is no exact science to this, as some titles are removed instantly without notice, whilst others do give a warning to gamers, or depending on the franchise, there could be a new iteration around the corner. This page should help you get the best insight into where to look for this info.

Depending on how recent the deletion was, and if the game was sold outside of Steam, you might be in luck. Some third-party retailers should still stock some keys, but you have to be quick as collectors snap them up. Older games are harder to find, and cost much more from grey key sellers or from other collectors. The main page contains a list of games you can still legally buy from reputable sites.