Sam and George are okay with Mace being alive.

I see an Echo-type scenario as a plausible approach.

Of course Mace Windu survived. He caught hold of a passing speeder while he was falling like Anakin did in Attack Of The Clones. I reckon he might turn up in the Boba Fett movie. Maybe Darth Vader finds out Mace is still alive and hires Boba Fett to track him down but Boba wants revenge as Mace killed his Dad so he wants to kill Mace himself rather than lead Vader to him?

Five-way fight: Zombie Mace versus Boba & Vader & Maul & Sidious. Later, Mace takes on Obi-wan & Yoda & Ahsoka.

I'll bet that Filoni's mind is churning away on Mace and Rebels crossover stories.