Forgtting combat power

[RainbowFury]

Scenario from munchkin bites!:
P1 is a werewolf with a total combat strength of 9 and meets lvl. 18 Azmodan.
P1 asks for help from P2 who has a combat strength of 12, so together they can beat it with 21 in combat strength.
P3 plays "undead +5 to monster"
P1 & P2 decides to run away because they forgot werewolves have +4 against undead, resolves the run away rolls and then realizes their mistake after the next door has been kicked down.
Question 1: should they be allowed to beat it since they technically could at the time?
Question 2: if P3 was aware of this when he played undead, and kept quiet, is that cheating or is it the players fighting own job to remember the +4 against undead?