Expiration of Apple developer account will cause App Store app to be down

Reference: https://developer.apple.com/support/ios/program-renewals.php

What happens if I does not renew my membership?

If your IOS Developer Program membership expires, your apps would no longer be available on the App Store and you'll not Be able to submit new apps or updates. You'll lose access to pre-release software, the Apple Developer Forums, certificates, Identifiers & Profiles, and Te Chnical support Incidents. However, you'll still has access to iTunes Connect and free development resources.

What does happens to my apps on the App Store if I does not renew my membership?

if your membership expires, your apps would no longer be available for purchase and would not appear in search Results on the App Store. However, if you renew your membership after it has expired, your apps would be available for purchase on the APP Store with In the hours. Need to resubmit your apps.