Totally ruined maps

A good friend of mine was working away for weeks on maps.He created a DM-Castlewars map,like the one from ut99,and was working on other custom ut99 maps from some of the best servers to bring them to ut4,and he got an error message saying some files were missing.He followed the correct way for fixing the issue,and out of nowhere he gets a blue screen ,and has to reboot.When he gtes back he finds all the work done up until that point was removed,even though it was all backed up in a different location.
I,.m writing this because he has completely uninstalled the game,and everything else…worked too long and hard,and it could have been the start of a new really cool server down the road.
why does this keep happening ?>

It is not frequent such issue and to be honest this is the first issue of this kind I read in the forums for at least 3 years (might lost one maybe). Dealing with huge amount of files needs version control software that will enable you to see what has changed between versions and pin-point whats wrong. A blue screen probably caused data to be written into disk to get lost causing inconsistency in the files and maybe even damaging them if the writing was interrupted in the middle. Raid disk setups would help eventually, being Raid 10 or 5 at least, so the damage could be even more mitigated or even completely avoided.
There is a chance the disk is damaged, thats why when he got the data back it was still inconsistent. He must use a tool to check the disk and maybe even format it again.