He comes back with Rey and everyone is fine with it
In this scenario, Ben Solo returns to the Resistance base with Rey. At first, everyone in the Resistance would be shocked to see the former Supreme Leader of the First Order and probably even would draw guns on him. After Rey tells them he’s changed and redeemed and even shows affection towards him in front of her friends and heroes of the Resistance, they accept him and celebrate the victory with him.
The film could then close with Ben and Rey together burying the Skywalker family lightsabers in the Tatooine sand. She could still proclaim herself to be Rey Skywalker as the two hold each other close watching the twin suns set.
The problem with this is that there would be no way in hell that Poe or Finn would be okay with this. Poe doesn’t seem to have the feels for Rey that Finn does, but is basically the leader of the Resistance at this point and would not be okay with the former Supreme Leader suddenly joining their side.
Finn would be in a jealous rage as he definitely loves Rey. Seeing her with Ben would put him in a frenzy and he would definitely be calling for his head. This is one scenario other than Ben dying that just wouldn’t work, as it opens up more story threads than it closes.