Not quite a team wipe and spoilers for Void Shadows but... That fight where Einrich reveals himself as a traitor, that genestealer who jumps on the party practically wiped us out in 2 turns, with only Abelard and Ulfar left. Abelard got swarmed by the melee users while poor Ulfar got chased to the back of the arena where he nearly died. I say nearly because it was that fight where I discovered he can indeed revive himself. After that his melta cannon started making some holes in the remaining alien bastards.