Supposing that there's something compelling each of them to make an earnest attempt at fighting everyone else with no alliances, Aradia and Bastion quickly devastate the competition. I think Aradia has the upper hand no matter what, but to what degree depends on how fast she runs out of time power juice. Tracer is a good counter for Bastion in game and Aradia can probably do a lot of the same stuff plus powerful telekinesis; however, she is not particularly bullet-resistant and can't pay attention to everything at once. If one of those two gets taken out before it's down to just them by multiple people attacking them at once or a lucky shot, the other definitely wins.

Everyone except Cirava has the ability to come back from death or survive intense destruction, so one possibility is that you're eliminated from the death match upon your first death (or incapacitation-that-would-be-death-for-most-people), like a much more brutal version of fighting to first blood, in which case Wilson and Thurlow retire to the stands to throw popcorn at the remaining fighters after getting taken out and Wormwood just kind of leaves. The other option is that you keep going until you exhaust your resurrective abilities, which tips the scale further in Aradia's favour since everybody else's is slower, more costly, and/or can be defeated by sufficiently chunky-salsa causes of death.