It's unquantifiable to say what he might have been had he stayed. But moving off 3rd was already locked in. I happened to be looking at career DRS for another player, and noticed that Devers was already up to #14 in negative DRS, and he has years to go. Had he stayed at 3rd, he might have been the #2 worst in history (behind Jeter).
FWIW, Bogaerts is #10 worst, and could crack the top-5 before he retires.