Maybe a wounded monster fled to another area, getting reinforcements. The PCs could have opened too many doors at one time. The PCs could ahve just blown their stealth. Or you did it intentionally because you're a Rat Bastard DM.
Either way, the PCs now find themselves in one encounter with two encounters worth of monsters.
When in this situation, what are the rules? What is the DM supposed to do, and what should he do?
Namely:
1) How is XP handled?
2) How about Healing/Encounter Powers?
For #2, would a short rest to allow the PCs to recharge encounter powers, but not healing surges be kosher, or should they be stuck with their normal encounter powers, and then tough it out with AWs?
1. Let the party run away
2. Depower the second group
3. Let them be overpowerd and knocked unconscious, all their gear taken and they are sold as slaves
4. Let them be captured and they are tied up with no gear and have to escape somehow
5. Let one party member survive to get help and raise them.
6. End of party, re-roll new
7. End of Campaign
You as DM do whatever you want.