I like the idea of S, D, and N ending the series alone. But it'll never happen.
Having had a papa who was a rolling stone, and having had dealings with young Carters, I'm only on board for Scarter IF he can stop wandering. Otherwise, I haven't seen enough in canon to give me any confidence in that pairing... Serena is still too damn wounded from her daddy to deal with a guy like Carter until much, much later, if ever. But it's a moot point. They're not going to get Sebastian Stan back. Instead we have S starting up what seems to be a serious relationship with a new guest star, which I have to admit is realistic for a girl of that age.
Also, having spent quite a lot of time on Twitter and FF lately, I find it telling that the root of the anti-Chuck and anti-Dan arguments are the same: he's horrible and he'll never change. Only the details differ. The difference is that Chuck realized he needed to change and made concerted efforts to do so while Dan thinks he's just fine, and others are the ones who need to change. And Dan would be the most likely person to make a statement that sets my teeth on edge: "What issues? I'm issue free." I hate when people say that! There is no such creature, not in real life, not in fiction, and Dan certainly isn't one. But to expect Dan to have a Chuck-level revelation of the necessity of personal change when he's had no external factors to nudge him in that direction (which in Chuck's case were anvil sized), is just strange to me. Chuck is a far more mature 21 year old than Dan or Nate, but hell, life's forced that on him.