If you deleted the disks without backing them up, you simply have 4-5 unusable certificates generated but not available for use because the private key is gone. If you continue to generate lots of certificates for the same domain and/or ip you may run into the Let's Encrypt rate limits and not be able to issue new certs. You can use the staging environment to test certificate issuance if you think you'll just be deleting the disks.
If you deleted them there isn't anything to do. Revocation is possible if you have the private key, but it's unnecessary unless you suspect key compromise.
you can reuse the certificate itself if that’s not compromised, but keep mind that your client won’t know about imported certificate and can’t renew until it has config for it (created a new cert or paste old renew config on it.)
I heard some thing like: Lets Encrypt will send email to remind me of certificates that are about to expire. If the certificate is permanent (), Lets Encrypt will remind me forever?
Let’s Encrypt will send you a few emails in the weeks before a certificate expires, if you haven’t already issued a newer certificate with the exact same names.
Even if you don’t, once the certificate expires, the email will stop.