Can someone just delete all the files?
Practically, only administrators can delete files. The worst a simple user can do is empty the page, which is completely reversible by any other user. Also, since in order to edit a page you have to be a member, the IMSLP administrators can track down the vandals and ban them from using IMSLP again, if they were proven to have acted maliciously and not accidentally. Vandalism will not be tolerated on IMSLP or generally any other wiki-based site.
