I think Schumacher has stated in the past he’s not into the idea of becoming a team boss. At least, that was around his Ferrari retirement.
More likely, he’d become some sort of ambassador to Mercedes, considering he’s already in their commercials, and is supposedly supervising some of their younger drivers. People tend not to mention Schumacher’s races in sportscars, but I think Mercedes could use his experience in a lot of fields other than F1 as well.
Truth be told, I don’t think he’ll ever race in another series. Maybe he’ll pick up Motorcycles again, but considering he is also a family man and has spent the last 21 years of his life involved in F1 in some shape or another, I don’t see it happening.