Exactly. That happened when I was testing a new backup EL39.
The cap came off the tube but there was enough wire on the tube to create a hook. I then soldered a skinny solid core wire to it. Cleaned the glass and cap and used some superglue gel to glue the cap back to the tube after threading the new wire through the desolder hole in the cap. Re-soldered and trimmed the excess of the wire. Back working now
The Mullards are a lot stronger than the EL39s but tend to leave them all in the adapters until they die. I also check for loose tops now and repair as above beforehand.