If Watchmen did return, what would be the plot of Season 2?
Watchmen Season 2 unfortunately seems like a far-off dream at this point, but we can't say it's totally off the table just yet. Lindelof told USA Today that he has "given [his] blessing" to HBO in case they wanted to green-light a second season, but HBO said that they wouldn't want to move forward with the project if Lindelof wasn't attached. It's possible that follow-up could come in the form of an anthology, which would make sense, considering Lindelof/HBO told the complete story the showrunner hoped to with Season 1. Bloys actually spoke to the thought of pursuing an anthology series -- and if that were the case, it's all up in the air what Season 2 might look like.
If by some surprising circumstance HBO did decide to tap back into that Season 1 storyline, though, it might explore whether or not Angela Abar (Regina King) inherited Dr. Manhattan's powers. If so, Season 2 could track her impact as a more involved superhuman, if the conversation she and Will Reeves (Louis Gossett, Jr.) had regarding Dr. Manhattan's ambivalence is any indicator. If she didn't end up inheriting his powers, we'll witness a world grappling with the loss of Dr. Manhattan.
There were also a few throwaway references to Dan Dreiberg (Patrick Wilson), the former Nite Owl II and Laurie's ex. After he and Laurie (Jean Smart) were captured doing vigilante work, Laurie joined the FBI and Dan went to prison. It's obvious that Laurie is still concerned for him, and given the numerous Nite Owl references scattered across the series and the unearthing of his ship in the season finale, it's well within the bounds of possibility for him to make an appearance in a potential Season 2.
Finally, it seems that Adrian Veidt's (Jeremy Irons) crimes against humanity would finally come to light. Wade still has his taped confession (the message to Robert Redford), and with Veidt in Laurie's custody, now may finally be the time that he's brought to trial and held accountable on Earth. In turn, we could see a world grappling with the fact that the biggest existential threat it's ever faced is nothing more than a hoax.
Don’t get too carried away with the theorizing, though -- HBO doesn't seem to want anyone else touching those characters if Lindelof won't. We'll just have to live with the near perfection and ambiguous ending of Season 1 of Watchmen forever.