If I wanted that to happen Swaggy, then there'd have to be a REASON to why we're battling more zombies. The again, on Modern Day - Day 34, Zomboss DID say that they'd meet again. Too bad PopCap isn't bothering to do anything about it.
You would say that Penny's Pursuit may have continued the story from there, but according to the post on the EA Website, it says that Dave and Penny were on BIG WAVE BEACH when all this happens. So basically, Penny's Pursuit should just be unlocked after freakin' BWB.