If you have a guy making 360 grand, and you demote him to aaa, will his salary stay at 360 grand for next year? Or will it revert back to aaa salary?

It will stay at 360 per year.

Disagree - I have seen both, depending on age, years experience and previous contract

Yeah, it reverts back to the MiLB salary. I do this at the end of every season with players that still have options left. It gives you alot more flexibility the next season as to who you put on the 25-man roster. The only time that it doesn't revert back is if the player was signed to a multiple year deal at the league minimum(i.e. IFA signed to big league contract).