He should be able to reuse all of his existing renders. So even if he's completely changing the mechanics and a lot of the story, as long as the scenes from the current version are still going to be in there somewhere, those are basically already done. So progress on the new version should be a lot faster than the current version until it at least catches up to where the current game is. Just my 2 cents.If I got it right then.
It sounds pretty bad if the pace is the same as now, it will take several years to catch up with the current version on the progress
After the release of the new version, the main question will again be when it will be possible to get rid of Eric.
That could still mean he's adding stuff in between the earliest content and the current endgame stuff but he doesn't have to remake the existing renders. He doesn't have to redo the existing dialog much if at all. He just might move things around, add certain mechanics, insert new scenes in between the current progression, etc.