There are a couple of alternatives available including MonoGame, and ANX. Searching to find the MonoGame website just now I also stumbled across MonoXNA, but I hadn't heard of it previously and don't know anything about it. Of the three, I believe MonoGame is the most stable and mature, so I'd suggest taking a look at it if you're not comfortable continuing to use XNA for now.
If you make a game in XNA right now, will it not be able to be installed on PCs?
Not at all, there's absolutely no reason you can't continue to use the existing XNA library for now, it just won't be receiving support or updates.
Hope that helps!
: Updated MonoGame link.