Weston, the man that's supposed to be in the jail cell on the southwest corner of Castle Britannia's roof, is missing. The jail cell is empty. I have not completed the quest to free him (i.e. spoken to Lord British about him). What do I do?

This actually happened to me last time I played, which was surprising cause it had never happened before in many playthroughs. I turned on the debug cheats, looked up his internal ID number online, and forced him into the party. This caused him to appear nearby and follow me, so I walked him back to the jail cell and removed him from the group.

You wouldn't know how to find Weston's NPC number would you?

This bug in general isn't going to stick to my save file is it?

At the time I was able to google a list, but having trouble finding it again now. Used to have one printed off ages ago. Anyway it never caused any further problems and Weston is really a very minor character. In fact, I'm pretty sure after his plot resolves he's never seen again.

You can look up any ID of an NPC using the [N] cheat. If you can't find his ID online the next best thing would be to start a new game and teleport over to Britain to check his ID. If you're curious enough you could [I]nspect his ID once you return to your main game to see where is and what he's doing that he's not in the jail cell anymore to boot
[url=https://tcrf.net/Ultima_VII:_The_Black_Gate/Cheat_Mode#.5BN.5Dumber_ID]https://tcrf.net/Ultima_VII:_The_Black_Gate/Cheat_Mode#.5BN.5Dumber_ID[/url]

When it happened to me, I tried teleporting to him and ended up stuck under the ground in a random part of the map, but there was still no trace of him there. Can't imagine what the cause could be. I've never seen this bug documented anywhere online so it must be very rare.