I would remind you that running many, heavily loss making lines was what led to the Beeching reforms.
Interestingly the railways now carry more passengers and freight than they did pre Beeching on a much smaller network, which proves the good Doctor had a point when he pointed out the inefficiences of what was there.
Continually sustaining bigger and bigger losses eventually leads to financial collapse - as many private enterprises can demonstrate so taking on more loss making activities is counterproductive.
So your answer for preventing another round of Beeching "reforms" (I assume you are referring to the disastrous closure programme that blights the country to this day) is ...... another round of closures. Twisted logic if ever there was.
The fact that the railways carry much much more traffic than sixty years ago does not prove that "The good Doctor " had a point. For this to have been the case, the increase in numbers would have had to have transferred from the lines that were closed. I would suggest that this is unlikely to be the case to any large extent, and that the growth in traffic is primarily due to the smaller network having gotten better at attracting more traffic. This is what is needed to generate more revenue, not another round of closures.
Mean while in the now rail-less areas where people haven't made it as far as the smaller network, the majority of those people who would have used the train are now car-dependant.
The Beeching reforms led to a viable and sustainable network - whether you like it or not. The fact is that only a tiny proportion of Beeching closures have ever been reversed, particularly where line reopenings are concerned and not all of those have been resounding successes.
Except increasing subsidies does just tgat, it's underpinning a loss making service. A loss is a loss however you choose tondress it up, therefore increasing subsidies just expands loss making operations. It's not difficult to understand.
Clearly, no it didn't lead to a "viable network". This is illustrated by the fact that the closure programme didn't lead to the railway paying its way, as was intended.
There was no end game or destination of a self-funding sustainable network at the end of it. The logic of it would have been to keep snipping and pruning away at the network until there was nothing left.
What actually led to the "viable" network was a political decision and consensus to stabilize the coverage of the network. This decision was taken in spite of the closure programme clearly failing in its aims to make the railway self-funding.
Also, the fact that only a tiny proportion of closures have been reversed has absolutely no bearing on whether the initial closure of any given route was a good idea or not. The only thing it proves is that it is very costly and difficult to reopen a railway line when it has been torn up/built over. A good illustration of this point is the number of routes that were listed for closure and are now thriving, such as the Marshlink. We know that it is a busy route because we can experience the passengers using it. However we also know that if it had been closed and torn up, it would be highly unlikely that it would be reopened.