I would prefer to change it to all senators except the one being expelled have voted.
But what if we have 2 simultaneous expulsion votes?
Well, in that case I guess there could be 3 possibilities:
1: Restrict expulsion votes so only one can be in the floor at any given time
2: Simply not care about this and wait out the 72 hours in the unlikely case that we have to expel 2 senators at the same time
3: Allow for expulsions of 2 senators in the same resolution, and do it so it's over when the other 4 senators have voted.