Ansom is taking a gamble. He's going to risk almost everything (all his forest units plus himself) to take out what he believes to be 3 warlords and a large number of weakened dragons. It hasn't even occurred to him that this is a trap, or that any warlords could survive if it wasn't. So he's not planning on retreat, he's planning on a glorious victory (complete with more Ewok victory music, no doubt).