Regardless how you feel about Simmons and some of his deficiencies, I think this Sixers team would function very well playing a more fast-paced game with a lot of transition. Basically, Simmons as the "QB", surrounded by a bunch of shooters, legit 3-and-D players and decent bigs (preferably more defensive-minded). And keep in mind Simmons is already a great defender and can only get better so he'll help defend other teams' elite guards.
I think if you could trade Embiid in some sort of package for someone like Beal or one of Portland's guards, that'd help. Now there's probably not much hope for Horford and Harris going forward, but you still might have to persist with them and hope maybe they can bounceback. Now that Embiid's gone in this scenario, maybe Horford can play more of his style on the team. Harris' contract is terrible but the Sixers and their fans love him. Things could open up and maybe he can do well next season if he can simply focus on scoring.
Sometimes I think when Embiid's out there, the pace of the game slowed for the Sixers even when Simmons was on the court. That's not their style. The 2018 style with Simmons running the show and perimeter guys like Reddick, Belinelli, etc. seemed to work well. Of course having a star and proven playoff performer like Butler like in 2019 would help immensely.
Long story short, in my scenario above you'd go into next season with something like:
Simmons/Milton/Burks
(1 of Lillard, CJ or Beal)/Richardson/Thybulle/Korkmaz
Harris/Richardson/Robinson(?)
Free Agent/Scott/Harris
Horford/O'Quinn/Scott/Pelle
And of course you could factor in a draft pick addition. I'll admit, that team could be fun to watch. They did mention over the season that Horford seemed uncomfortable with his role. Now with Embiid out he could play his style more at the 5. They'd probably want to add a FA big somehow as well. Bench might still be thin but that's a great starting lineup if it can mesh well, and guys like Milton, Thybulle continue to improve.