If the TOCs and unions (TSSA particularly) persist with their hostile approach to passengers, and the requirement for masks remains, a hell of a lot of people will be put off using trains. I am one - if I absolutely have to I will use them for work occasionally, but not otherwise. The railways are digging themselves into a hole with their messaging and rules - but will no doubt be surprised if passengers don't return when they decide that the want them back again (which will probably be once the financial responsibility passes back to the franchisees).
If they went back to business as normal, I would go back to using them straight away, but at the moment I'm planning things to avoid travel, and if nothing has changed by the time I have to start travelling more again for work then I'll have to buy a car (already been looking round local second-hand car garriages). If it gets to that stage I won't be going back to the railways again other than occasionally.
I'm not even sure that the current paranoid approach will encourage those who are overly fearful of the virus - many will probably still see public transport as too much of a risk and avoid it.