Unlike other industries, and with reference to front line staff especially, on the railway there is no backlog of passengers waiting to be moved after the strike has ended. They, and their money went on the strike day by other means.
Similarly for freight. Most freight went on the day by road, possibly with the customer having to sign a 12 month contract with a road haulier to get his service, so future traffic is also lost.
Any overtime staff get due to endemic shortages in the industry is overtime they could have had with or without a strike.
I can say with certainty that a lot of freight traffic was lost for good, like that, during strikes in the past. Pretty heartbreaking when you'd put a lot of effort into getting it to see it thrown away, and had no benefit from the strike...
Although I was almost always a freight man, I did notice that, after a strike, passenger trains were noticeably more empty for months afterwards - I did wonder whether the (slow) recovery was actually due to new customers reaching working age replacing ones who had been put off the railways for good. In the those days, there were many passengers who had no choice but to use rail but had a deep seated, bitter resentment of B.R. and its employees (railway managers never talked shop on a train, you would have soon got into a heated argument, I've seen it). I don't think the railways have such a monopoly, now though, particularly with W.F.H..
There may be a more direct affect on, for example, drivers now compared to B.R. days., Back then, if turns at a depot were reduced because of loss of traffic the effect was spread over all the drivers (in reality, less overtime). Nowadays, the employment is much more flow - specific, so that if a freight flow is lost the dedicated drivers will just not have a job. Similarly, the number of drivers jobs in the T.O.C.s is directly related to work in that particular line. Might still, of course, mean no overtime rather than redundancy.
But my opinion contradicts that of the driver who posted that 'don't worry, all the traffic would come back'. Sorry! We'll see...