I had decided to use an angle grinder to cut off the bolt on a pair of French doors that could not be retracted either with the knobs or internally once the knobs were removed. This AM I set up a light so I could see well, measured (on another pair of doors) the depth of cut I needed and marked it on the cut off wheel.
Then it occurred to me that if a 1/16 thick cut off wheel would fit between the doors, so would a knife blade so I grabbed one, and tried to move the bolt with it. It moved. Got a second knife, moved and held the larch bolt with the first, moved it some more and held it with knife 2, some more with knife #1. Et cetera. Four or five seconds and the door was open, no cutting necessary.
After that, the latch bolt seemed to be fine' both when pushing it from the end and from the inside where the knob would normally actuate it. No idea it got stuck...it was a bit gunky but not all that bad.
Anyway, the new lockset is on and I have the old one for a spare should I ever have need. If I can remember where I put it :)