I suppose you have no backup from which to recover. In that case, it is important to understand that membership and participation in your Puppet site hinges on recognition of a common certificate authority. By default, Puppet uses its own CA and a self-signed CA certificate; such a certificate cannot be regenerated if it is lost.
If your CA certificate was indeed lost (or even if just the private key was lost), and it cannot be recovered from backup, then at best your site is crippled. You will be unable to authorize any new agents. If you also lost the master's certificate then you are completely toast -- there is no way to authorize or re-authorize a master that the existing agents will accept without reconfiguration. In this case, your only viable course of action is to re-authorize all your agents against the new master and its new CA.
If, on the other hand, you still have at least the CA certificate then you can probably recover. I cannot provide details, but I don't doubt that there are those around here who can.
John