If a journey of some length needs to be made, it needs to be made. It is better if these are minimised, but in my view many companies and individuals already had policies or custom and practice that longer journeys need to be necessary to the job before being accepted. Currently, lots of otherwise necessary work is suspended, so the associated travel has been cancelled. We will return to a situation where this resumes, it's just that it's likely that places where this culture wasn't strong will have it more strongly. In business, there are times where more travel is more efficient because it avoids any staff being placed out overnight, among other things.
Once that decision is made that the travel is actually necessary, how it is is made is always worth pushing away from cars and aircraft onto trains. For some journeys obviously some of those options don't actually exist, but where there's a rail service that's viable, it's worthwhile to encourage its use.
Long leisure journeys are 'necessary' in a very different way to business travel. These will continue to be made.
In my personal example there are unlikely to be changes to any of my work travel. I already travelled only where necessary, and this tended to take the form either of site visits or full-day meetings. These are infrequent for me by their nature and it is not likely that these will be reduced.