Cash will be more important. It’s priority #1.
Both are linked (i.e. you need bums on seats to get cash), however annual season ticket holders get some significant discounts.
To illustrate this of you WFH 3 days a week and commute between Southampton and Winchester your annual rail costs fall from £1,000 to £700. Therefore you've reduced your rail use by 60% but only save 30% (assuming all anytime travel).
Whilst that's money that the railway would need to get back there's now more capacity to carry more people.
With one person doing that it's not going to make much of a difference to capacity, but if you have about 1/2 the people doing it then a train which was full with 1 person standing for every 5 seats would then actually have 3 spare seats for every 20 seats. Whilst that's not going to be great levels of comfort it's a lot better than it was.
Also it's worth noting that people who WFH a lot more (say, a few days a month) aren't likely to carry on traveling in from Epsom when they could travel in from Exmouth and have a much better quality of life. If that happens then they could even end up paying broadly the same amount of money to the railways, as the savings to them would be on house costs (look at the prices of comparable homes between the two). Especially if it allows them to make that move a few years before retiring and gain some of the benefits early.
For instance being able to walk with sea views after finishing work at 6pm, rather than have an hour's worth of rail travel before being able to do anything. During the summer you could still eat at the same time as you always have but having got a sea swim in between finishing work and eating.
If you really wanted to, you could even WFB (Work From Boat) with days that you're just working on reports/replying to emails taking your boat out and using 4G for updates and then going for a sail in the evening. You could even do that for a few days at a time.
The political fallout from trying to close branchlines would be significant, especially if they hadn't seen much of a fall in traffic. Questions like "why wasn't this being looked at closure in 2012 when we had lower volumes of passengers than we have in 2021?" probably wouldn't be the best starting point. Especially when most of the falls in passenger numbers would be in the South East.
Given the flack from "London cast offs" when trains get moved North, of the North has to bear the brunt of service reductions because of falling passenger numbers in the South East that's going to be a whole other level of flack (says someone who lives in the South East!!!)
Anyway with the target of 68% reduction in emissions between 1990 and 2030 and transport being about 1/3 of all emissions, any cuts to rail is likely to harm the ability to meet that target.
As whilst average rail emissions are comparable (per mile per person) as EV's that doesn't give cars much scope to reduce from that figure (other than greening the grid), whilst rail has scope to do so to a much bigger extent. That's before you consider that someone using rail is more likely to walk/cycle more of their up to 3 mile trips than someone with a car and so it's likely that a person using rail would be traveling less miles overall.
