I think the final episode of Sunny in Philadelphia should be "Dennis kills the gang"

With their character development I think it's the only logical ending. He makes it look like Charlie died from mislabeled fridge poison, frank "accidentally" shoots himself, Dee commits suicide, but then he leaves Mac alive until Mac comes out as gay and confesses he's been in love with Dennis all these years, then Dennis makes it look like he died in a Project Badass stunt.

Then Dennis drinks a beer at the bar alone, completely content and shrugs.

Edit: Oh and Dennis tells Mac he murdered the gang and a conversation similar to "the implication" discussion where Mac says its fucked up and Dennis patiently explains how annoying everyone was and how they'll totally get more chicks with just the two of them. This is where Mac will segway into "plus no one is here to judge us for being together...."