I think The Purge only ends 1 of 2 ways for our 3some. Either Jenna dies and Rick and Lila have to deal, or Rick and Lila die and Jenna’s left alone. On the flip side, I could see just Lila dying as methinks she had all this planned (party shooting + we happens in 1×08-1×11) to get Jenna to herself so that they can go save the world on her dad’s money without Rick. Dad and Mom dead = lots of money. Get into R&Js house to get Rick killed = Jenna to herself.

Sorry, forgot to reply earlier, but yeah, I don’t see any kind of straightforward “happy” ending. I think the show definitely wants to punish shitty people, hence the NFFA massacre and David, and if Lila has been manipulating people and using the purge to enact her own plans, she won’t get away with it.