That’s a very good question which I don’t have an answer to as I haven’t tested it. If the TV connector did automatically combine the channels with only one HA then that would mean that, if possible, putting one of the HAs in flight mode would give you exactly what you want.
The TV connector does seem to stream to each side independently but that is in a setup where the Phonak system ‘knows’ that there are two HAs available. Not sure what would happen in any other scenario.