None of us really know the exact reason Shildt was fired. I never really got the impression it had anything to do with Reyes. Friction with Jeff Albert, Mike Maddux, and/or the analytics department seems more likely to me but who knows?
As Brian stated, whatever the reason was you can be sure that Shildt is aware of it. You don’t make a decision like that with a manager with his w-l record unless there was a significant difference of opinion.