Was it a wildcard or server specific certificate? In order to import the certificate, one of the following must be true:
- A CSR (certificate signing request) must exist on the server for the certificate.
- You must have the private key that corresponds to the certificate.
If it is a wildcard, you can export the cert and private key from another node and import it to the node you had to reload.
If it is a server specific certificate and you don't have a copy of the private key, you will need to request a new certificate as you won't be able to import the certificate.
That's probably not the answer you were hoping for. For future upgrades, be sure to obtain a backup of the certificate and private key (not just the certificate) from each node before you begin. It will save you from this kind of situation.