The implosion I think so--but it seems we are moving towards heat death or a big rip.
I think the Douwds have the best shot at the Q. The Organian attempt to stop conflict and the Excalbian attempts to foment it cancelled each other out, according to DC, leaving things freer.
The Excalbians weren't on the high-end of powerful beings in Star Trek. At least, nothing that was shown depicted them as such. Sure, they had strong mental abilities, but so did the Talosians. The Organians could easily defeat the Excalbians in a conflict. I doubt they would 'cancel out.'