What happens if we can't get to it by Mar 31, 2021? Does push notification stop working on existing published apps in Appstore? will current apps be pulled from Appstore? Will Apple simply reject new apps being uploaded that aren’t setup with new APNS key?

What happens if we can't get to it by Mar 31, 2021? Does push notification stop working on existing published apps in Appstore? Will Apple simply reject new apps being uploaded that aren’t setup with new APNS key, will current apps be pulled from Appstore?

Yes, https://developer.apple.com/news/?id=c88acm2b