Zaluzhny is likely his biggest rival in any coming election.
Most likely candidates for replacement of Zaluzhny are military intelligence wunderboy Budanov (who is my age), or Moscow-trained Syrski.
I don't know, which is better for Russia.
Reasons for their candidacies:
1) Budanov is the architect of what remains the only theater of this war, where Ukraine continues to exceed expectations - namely the maritime domain. He runs the "Russian" neo-Nazi groups which are used to make raids into Belgorod. He commands the drone strikes across Russia. It's not clear if he's able to competently command even a company in the Land Forces, let alone strategic-level front maneuvers, but he does have all those other achievements.
2) Syrski already commands a huge part of the Ukrainian military, specifically their ground forces and the entire Eastern theater. Though not very popular with the troops (he has the reputation of a butcher), he's much more media shy than Zaluzhny and seems to know his place. He's also Zaluzhny's old boss (Zaluzhny got promoted over him b/c he went to school in Odessa rather than Moscow).