I don't think any of us really know what the long term impact is going to be.
Whilst I can see the rational for permanent increased working from home, it does have limitations. It's cost effective for sure, but there are efficiency penalties.
Before this situation, I had started thinking about looking for another job. I currently work from home and have done for a few years. I miss having colleagues, the work environment have it's much more difficult to just chuck ideas around and think aloud when working remotely. I can also find it hard to focus at home, and there is constant distraction from Mrs Trebor and kids at present. I was doing a trip to Sleaford once a week before lockdown and found the 2.5 hours each way on the train amongst my most productive hours in the week - bag a table and get a load of work done with little distraction.
Whilst I can see some of the more transactional roles having at least a proportion of home working in future, I suspect most will migrate back to the office. Plus for factories etc, they just can't be effectively run from a distance - management as well as front line staff will always be site based.
I think it's safe to say that there will be done permanent reductions in demand. How the industry responds will be interesting. Maybe more/better first class, perhaps with compartments as mobile office space. Or retrenchment and closure of done routes. My nightmare scenario is HS2 (to the extent it gets built), commuter routes around major cities and a few long distance routes retained with everything else gone. A Serpell + HS2 situation.
One thing I'm sure of is that talk of social distancing and 20% load factors to allow it is balony for anything other than the very short term. Might as well shut the railways completely in that case.