User blog comment:Mr. Mittens/Thanks, Guys/@comment-2250460-20120918195528/@comment-4721065-20120921103658

How exactly would effects of Synthesis fade away? The galaxy's eenizens DNA is rewritten; the only way they could retcon it out is if the sapient species didn't like it after all and developed technology to revert to their previous state (something which would undoubtably piss off the people who have chosen this ending.) It's not as bad in Control, where you can just say that Shepbringer got tired of looking after the galaxy and retreated somewhere else (of course, if the writers are feeling evil, they could have them suicide.) Overall, not a good idea by any means.