Did he just get someone to fill in for him and leave you guys to fly blind? that would tick me off.
There should have been arrangements made, all I could advise is to look into billing Locum Tenens which allows for a substitute to come in and provide services billing with their own NPI, etc for up to 60 days I believe. The Q6 modifier is needed. There are certain requirements that have to be met for a provider to bill under Locum Tenens and some are specific to Medicare. One of them is that the provider filling in must be credentialed with the carriers and I believe with Medicare the Locum Tenens physician cannot have his/her own practice. I would research this a little bit. I only billed for one group that used Locum Tenens but they had everything setup ahead of time for us.
I remember that the group also ended up having a problem with their malpractice carrier because they didn't have coverage for such an arrangement.