Ok simple question. If defense plays the Loser Wild Flare (Everyone Loses and all ships go to the warp) and the offense plays the Loser power (winners lose and losers win) what happens? I personally suspect that the flare ends the encounter and everyone loses, but offense effects happen first, meaning that the loser declares an upset before the flare is played, and the loser power says that the upset happens after all other effects are adjudicated. One of my players insists that this means that everyone wins (whatever that means). Is there a definitive ruling on this that I can point my player to?

Your friend is incorrect, and the texts prove it:

Loser: As a main player, before encounter cards are selected, you may use this power to declare an upset. Once an upset has been declared, both main players must play attack cards, if possible. Then, after cards are revealed, the winning side loses and the losing side wins . This occurs after all other game effects are resolved (such as the Human’s power being zapped).

Wild Loser: As a main player, before encounter cards are selected, you may declare that both sides lose, sending all involved ships to the warp.

Point out to your friend that, although the power and the flare both activate before cards are selected, the flare ends the encounter in the Planning Phase, before the power gets a chance to affect the outcome (in the Reveal or Resolution Phase, which never occur due to the flare).

Sorry, upon re-reading I realized you already knew most of what I was saying, and I should have made my answer more concise:

Just point out that the Loser power cannot actually flip the outcome until after cards are revealed , so if cards are never revealed then there's no flip. (Clearly when the Wild Loser is invoked, cards are not even selected, let alone revealed.)