My filament had a snag in the spool and I ended up ghost printing the head of my Yoda… 
What I ended up doing is measured how much was printed successfully and then lowered the STL by that much in my slicer and printed and glued back on… after painting it turned out great…
I ran into a similar problem last week. knew i was about to run out of filament so I went to change the filament but when my printer restarted it was slightly out of alignment on the new lines. It was disappointing. so I aborted the print. then in PRUSA slicer I cut the model at the last printed line as per the display and started printing the top bit separately. I plan on crazy glueing or 5min epoxy the two pieces together. way better than having to toss the print especially with it having already been a 20 hour print. it will be sanded, filled and painted anyway so should be invisible when done.
Absolutely excellent solution. Everybody should read this before tossing a potentially failed print!
