775 (meaning owner/group read/write; other read) 750 (owner read/write; group read; other none)
If snapshots are visible, you can do restores yourself (by copying the file out of a (normally hidden) .snapshot copy of the directory. If they're not visible, you can request a restore to be done, usually within a few hours of your request.
The reason we disable snapshot visibility on qtrees holding home directories on the faculty, research, grad and ilab clusters is for the protection of potentially misprotected files. Suppose you create a file, "secret" and put your bank account information and password in it. Later, you realize you left it protected so that anybody could read it, so you reprotect it. The file is still publicly protected in any snapshots in which it exists. Someone browsing through the snapshot copy of the filesystem will still be able to read the file. Even privileged users cannot change (eg, change permission or delete a file) in a snapshot.