This has actually happened to me several times... My only feeling was utter despair, as I had no backups whatsoever (that was when I learned the importance of backing up your songs folder). The time it happened after I only lost a few gigabytes of storage. But yeah, there was a lot of head banging/scratching that day.
Edit: Originally lost about 30 gigabytes I believe.
I mean if it was just deleted I suppose I would be a little annoyed, but it wouldn't take long to get all my songs back. If it was deleted for good, I'd probably be sad .
I wouldn't be too mad, since I already have my skins and replays uploaded on MEGA, and 95% of my maps come from a very large beatmap pack, the only thing I would be mad about is re-configuring all my settings lol
REEEEEEEEEEEEEEEEEEEEEEEEE MY LOLI SONGS !!!!!! J SNDK:LJSDD FSDJF NSDPO: FNDSOF SDODFASDSAD
(then prob just open my bookmarks and download all of em one by one again QAQ), while forgetting that I didn't even download the client to actually process the beatmaps