Hi @Kox
I do not understand how he can have been issued with a residence permit if his wife, the EU citizen, never worked in Germany. The main requirement for non-EU spouses to receive a permit is that the EU citizen to be working or have worked in the past. There are special rules according to articles 20 and 21 of an agreement called the AEUV for couples with children but those permits are for very specific cases.
I assume the card was issued in 2018 for 5 years and is now expiring. Once he has been working for 5 years as a member of an EU citizen he has permanent residency in Germany. He needs to request the confirmation of this from the Ausländerbehörde once the 5 years have passed and be issued with a ‘Daueraufenthaltskarte’. This status is different to the standard types of permanent residence (Niederlassungserlaubnis or Daueraufenthalt-EU). However, as I explained above, this status is usually after the EU citizen has also been working during the time. He needs to clarify how he was entitled to a permit if she was not working. Knowledge of the German language is not required.
If he is not entitled to permanent residency and she moves away, he is entitled to a new permit as long as he is working. For now, they are still married and still both resident in Germany. I therefore recommend he applies either for an extension of his current permit or the confirmation of his permanent residency as family member of an EU citizen.
Best,
Éanna