If a MLB player is signed to a guaranteed contract for 5 years but decides to retire after 3 years not due to injury and he is still physically able to play is the contract still paid?

Answer 1

No. If a player elects to retire he is placed on the "voluntary retired list" and is due no further recompense under his contract.

Should he elect to unretire his rights are still retained by the club with whom he was signed when he went onto the retired list.

It is for this reason most players file for free agency when they retire.