Incident-to is typically for non-physician providers (NP, PA, CNM) to bill under the physician if certain requirements are met. While it is not prohibited to use physician incident to services, it is not really the intent of incident-to. All that aside, if the physician has left, how could you possibly meet the incident to requirement of the billing physician being onsite and immediately available? It would also prohibit the temporary physician from seeing new patients, new problems, or conditions without an established plan of care.
Locum tenens is permitted for vacancies and seems to be an option. The 60 days starts the first day the temporary physician is used. It's not 60 random days. It's for 60 consecutive days. I do know at one point during the public health emergency, the 60 day limit was lifted. I do not know if it has been re-instated and you should confirm with CMS.