Saving in NWN 1 is EXTREMELY robust.
I have been playing the game for 15 years, on many different hardware setups on different computers with several different versions of Windows. much more than 1000 hours of playtime, multiple play throughs of all the original campaigns, and 50+ community mods..
Never had a single issue with quicksave.
I couple of issues I have seen reported rarely:
1: GOG Galaxy Cloud save feature seems less robust. I would NEVER use this feature. In an effort to synch saves, it apparently overwrites/deletes them sometimes. I never experienced this because I don't use GOG Galaxy at all.
2: People mess up their installation and don't have permissions on the save directory and can't write to it.
3: People misunderstand NWN quicksave. They think they get different quicksave slot for different modules or characters. There is ONLY one global quicksave slot in NWN, Even if playing a different module, quicksave will overwrite quicksave from different campaign/module/character.
Given the Above it is wise to:
1: Make sure you use standard install outside of protected file space (IOW don't install in the Windows directory).
2: Don't use GOG Galaxy in conjunction with NWN (or at all).
3: Don't rely on Quicksave since there is only 1 slot. Unless you make routine manual named saves, you can't backtrack beyond the last save.