Can't we somehow 'magic jar' him??
I'll carry him in my undead chest cavity for safe keeping, just incase he returns?...
If, when we get to the city, he somehow becomes comatosed (magic, disease, magical disease?? clutching straws!!), could we not sort something?
Maybe the easiest thing would be for his character to recieve a full-pardon and be offered his old job back?? Probably the quickest fix, but then we've no translator - though that shouldn't be a problem for too long, surely we can get some magic items to help out.... like legacy weapons, perhaps?... (hint, hint!) or maybe just a simple ring?