One more thing to think about here is that if you've knocked out all the synapse creatures, then they may flee and end up not capturing anything anyway, right? Granted if they come in on the last turn then they can capture, but if there's still a turn left, then they will almost assuredly fail a morale check at 5.

Alternatively, if you refrain from killing that last gaunt in a WON unit, then they can't come back until he's wiped. Not easy if they're in CC, but if they're just sitting there, you might be able to wipe it at the last minute. Much of it depends on who gets to go last, of course, but those are just some thoughts.