Can you imagine somebody getting to a railway station either having missed their train or to find it cancelled, simply walking away (especially if they are on their way home) whilst other trains then depart with 75% of their seats empty? If there are trains, unless they are physically prevented from doing so, people will board them. We need to get real about this and not idealise about a model that has no basis in reality.
Actually that's a really good point. I hadn't thought about cancellations. What would happen? Refund, but barred from entering next service if fully booked? Can't see them turfing people off the following service to allocate seats for those that got cancelled. Of course having travelled on many CrossCountry services, it's quite common to find many seats which are reserved and yet no one turned up to travel. So the train may even have enough capacity in reality for other travellers but be fully booked on paper.
I have to agree, the longer the situation persists, the more chance public transportation in all forms - bus, train, tram, coach, boat, plane etc. is simply going to be decimated.
Businesses can only run if the books balance in favour of profit, once they flip into loss, it can only be sustained for a certain period (even with bailouts, furloughing, loan assistance), there comes a day when the bills have to be paid. If commuters can't access or rely on the services to get to work, then they simply won't use them. If they aren't used, then the money doesn't come in and one day, sooner or later, the administrators get called in and the business closes down.
Problem is, when rural or less competitive routes go, they generally go for good.