After thinking about it for a while, I came up with an alternate defeat for Palpatine, that fits with both Rey and Finn’s character arcs:

Sometime during the final battle, Finn and Jannah hack into the main Star Destroyer. They deactivate the microchips that are making the Sith cultists obey Palpatine, and when the chips are deactivated they obey Finn instead.

Meanwhile on the Sith temple, Palpatine is trying to convince Rey to strike him down (Ben doesn’t go to Exegol in this version). Just when Rey’s about to kill him, she senses Finn, who tells her that they’re about to fire the Sith fleet’s main cannons at the temple, killing Palpatine. He tells her to get out before it’s too late.

Palpatine is frustrated at Rey’s delay, and orders her to make the sacrifice. Instead, she puts her saber away and says, “I won’t kill you, but I’m not going to save you.” She runs away as fast as possible, leaving a bewildered Palpatine to be annihilated by his own fleet.

It’s kind of rough, but I think it works. It allows Rey to fulfill the Jedi teachings, and it gives Finn something important to do for once.