If I'm going to be honest, it seems to be mostly a plot armor sort of deal. He needed to survive until he finished his story (even if his end was rather tragic) so he does. That being said, I thought I might have remembered some sort of statement about him being 'way faster than he looks' after that fight, implying that he might have just managed to escape more or less on his own merits. They could have made this more clear by having the WoL offer to go after him and then have the other Xaela say something like "we'll take care of it" though.