savegame duration

Depends on the game. If it has steam cloud support, the save will wait for you to reinstall the game at a later date. If not, maybe use save game manager or something, or manually backup saves.

Depends on games - If they use steam cloud or you will save them on hard drive - you can come back to them later.. Although some games can make saves not working after updates - especially if it's early access.

I don't know about steamcloud, but I would recommend making a manual backup of your save just to make sure. I make routine backups of every game I play as I am playing to make sure I don't lose progress if anything bad happens or so that I can go back if I really screw something up in the game.

There are a few different places the game can store the save file. If you don't know where it is, most games will have the location listed on the pcgamingwiki page for the game.

While it's possible to intentionally or by mishap delete or overwrite your cloud data, it will not disappear on you on its own. As per the defined concept of "cloud storage", steam's cloud saving stores your saved game data to external servers [in this case, dedicated Steam servers] after which it pulls the data by account access. In short, so long as you don't lose access to your Steam account or to the games in question, you should always* retain access to your cloud saves (as they don't expire on their own, and are in no way related to the state of your local storage).

*[barring the circumstance wherein you've disabled cloud syncronization for the game]

Some games, especially older ones, only store data locally. Likewise, there's always the very small possibility of an issue occurring with the stored cloud data (due to syncing errors). Save game data is usually incredibly small on storage space [given that all a typical save file is is just a text file with a few short notations in it], so if you're willing to put in the effort of hunting down the game's save file location (a google search will usually quickly give you the info) you can feel confident that your save data has been backed up.

That said, generally speaking, you're safe to just uninstall any game on Steam without too much stress, between the fact that the significant majority of games have cloud storage enabled [of course, as noted by users above, there are ways of quickly checking if a game lacks cloud support before uninstalling it] and the fact that issues with cloud saving are, to my knowledge, pretty much unheard of**, excepting for users who regularly play in offline mode or on multiple computers [ie, situations wherein syncing may not properly recognize the most recent progression state, overwriting such with less recent data].

**[Though, for caution's sake, you'll probably want to avoid relying too heavily on anything that relies on Steam server access during a Steam Sale, given how problematic server connections can be during those.]

Depending on the game, when it updates, the savegames become incompatible.
So keep that in mind! (usually for the more niche kind of games, Dwarf Fortress is an excellent example of this)