At present we only compare sha1 hashes and files sizes, but we do not try to recover from content file corruption or other problems.
We could probably do a lot more when we detect problem:
1/ if we have new file content and detect problem we may try to fix current issue.
2/ we may look into files table and lookup more information and validate existing content
see http://moodle.org/mod/forum/discuss.php?d=202934 for related info