Partial as I suspect it might not be much clearer until there is an official statement about this, likely around 27th December:
Straight off the bat, this article says this:
Without a functional external radiator, there are concerns about the interior of the Soyuz spacecraft overheating. This could damage sensitive flight computers, necessitating a manual re-entry into Earth's atmosphere. Much of the work over the next week will likely be conducted to understand how the spacecraft's internal temperature will change once it departs from the space station.
the accident in the thermal control system of the Soyuz MS-22 is serious and can lead to the failure of the ship's instruments - it will overheat on the sunny side and freeze in the Earth's shadow while orbiting as part of the ISS. Now Roscosmos specialists are considering priority measures to ensure an acceptable thermal regime for the operation of instruments on the ship.
The latter seems to suggest that keeping the Soyuz attached to the ISS in this state is a risk to the entire station, so undocking it uncrewed is likely one of those options.