If the file is truncated though, it means the file has been shortened. The data in it is badly damaged and it is unlikely to be recoverable.
nfixup.exe will tell you.
At that point the best things to do are:
1- get a backup.
2- retrieve backed-up journal files, research how to put these together with your last backup, and derive as close a match to your existing database as allowable.
With those, you'll probably need a bit more experienced Lotus support than I could muster on my own. But I've seen it done. It's possible to do it.
If the NSF were only corrupted as a result of a crash, the journal might just be able to rebuild the database without further comment.