The fact that saving and reloading doesn't lead to a perfect reset anymore should be completely and utterly terrifying to him. It's his only tool for surviving this world by letting him get out of otherwise hopeless situations.
If he loses the ability to predict actions from saving and reloading, he's effectively playing a new file all over again (if not worse since it seems that certain characters are actually AWARE of past iterations).
It's not a matter of slight divergences due to actions taken after reloading; it's the divergences that are occurring due to actions taken in the pre-loaded timelines that are abjectly terrifying, because it now means he needs to manage his actions perfectly *across timelines* without the backup of reloading to fix mistakes.