I can see your point, although if they received a 7th penalty on behalf of their team during a Jam they would be able to serve it. Either way though, the initial dilemma remains unchanged.
I agree a new Captain can be selected before the next Jam starts if they want or need to, however that doesn’t change the fact that the old Captain still received the penalty and fouled out due to it. Therefore normal substitution rules seem to apply. I don’t see anything that says a Captain’s substitute has to be the new Captain, only that they must be in the same Role (Jammer, Pivot or Blocker).