Playing devil’s advocate: Let’s assume a Borg nanite could assimilate a Q while it/they assumed a corporeal form. Depending on it’s collective/queen’s objectives, it could wreak plenty of havoc across known time and space. But we’re dealing with the Q here, so at any point they could “assume control” switching from chaotic good/neutral/evil as they see fit. After allowing the collective to have it’s fun, with a snap, we’re back to square one. In the event of actual assimilation, let’s just assume the known universe is kaput. Take your pick.