Would Desantis appoint him?
Possibly.
Matt Gaetz managed DeSantis' transition team when he was elected governor. He has called DeSantis “the best governor in America” and has said he would've been the Republican Party’s presidential nominee in 2024 had Trump not jumped into the race.
It's widely expected that DeSantis will fill Rubio's post with a loyalist.
Gaetz would fit this requirement.