Moved to Help because Off Topic is not a good place for this thread.
First I'd like to mention that Xasuma has a download link to all of his beatmaps linked directly on his userpage. If you want to download them, that is where you can find them.
Second, osu! should not just randomly uninstall itself. You can, however, have multiple osu! installations on your computer, and more often than not when people think their entire game was completely deleted somehow, they really just managed to install the game to a different location and open that instead (settings, maps, skins, etc. are all stored on a per-installation basis, so you can have separate sets of everything if you want).
I suggest you look through your computer's files first before spending the time downloading xasuma's file, remaking skins, and all of that jazz. The default installation location is
C:\Users\<Username>\AppData\Local\osu!. If you didn't change that when you initially installed the game, it should be there. You can also try using
windirstat as well, if you had 30k+ beatmaps it should be pretty high up on the list.
If you have thoroughly looked through all of you files and you really can't find it anywhere, then I'd also highly suggest running some antivirus scan, because you probably have something on your computer deleting your files without your knowledge.