What I've always wondered is how it works when players get called up and sent back down to the minors

I think it would depend on the contract provisions.

Generally, when a player is called up from the minors, he gets the MLB minimum unless he was making more already (which is the norm for highly regarded prospects), then he continues to get that higher amount. I think that if he gets sent back down, he still gets the higher of the MLB minimum and his contract amount.

If a major league player is sent down for rehab, he usually keep his salary.

Christina