Essential travel will always be necessary, otherwise it’s not essential! Essential travellers use the sleeper every single night, as they have done since its inception. There will continue to be many people who require the sleeper for essential work commitments, medical reasons, funerals etc, regardless of whether there are tourists on board or not.
This is why I am slightly puzzled by the decision to remove the Glasgow Central portion of the Lowlander, and not to reinstate the Aberdeen until September. I would have concentrated for the moment on the portions which are useful to essential travellers/workers, and left the Fort William until last to reinstate (if, for whatever reason, it was impossible at this point to reinstate a full service), as Fort William is the least useful to essential workers. That way, CS ensure the goodwill of essential travellers who will use them come what may, and fulfil their social function.
I don’t think it’s a good idea in this current climate to prioritise tourist traffic, especially when we are being asked to avoid using public transport for leisure travel.