I don't think the shareholders in the UK freight companies care much about the drivers who operate their trains and their complaints. At the end of the day they're very reliable and get the job done, unlike the British products of similar vintage. Their biggest black mark would be fuel efficiency of course, hence the small renaissance of the 60s.
The mechanicals will keep going, parts support is always going to be first class and the bodywork will always be cheap to mend when it comes to corrosion. Once fuel stays on the cheap side they'll be favoured for a good while yet I reckon.