I was returning from Sheffield to Newport via Stockport that evening, and got caught up in this.
The first leg was okay, but as the Carmarthen train was approaching Stockport, the destination on the screen suddenly changed to Shrewsbury! I asked one of the platform staff what was happening, and he asked one of his colleagues on his radio, but neither of them knew. The announcement said "the next train is for Carmarthen", so I was advised to get on, which I did.
Something like the same thing had happened at Wilmslow and the other stations before Crewe, as I heard at least one conversation arranging (or trying to arrange) personal transport from Shrewsbury. When the conductor came around the train just before Crewe, I asked him what was happening, and he promised to find out.
When we left Crewe, he made an announcement that the line was closed between Shrewsbury and Hereford because of a signal failure. There would be some alternative transport between these two stations, but none to destinations after Hereford. Passengers travelling beyond Hereford were advised to go to Birmingham and down to Newport.
I'd have to say that the conductor was very good. I asked him for the times and he said I'll print them out for you, which was very helpful. I had a 50 minute wait at Shrewsbury before the train to Birmingham (filled by two very welcome pints in the pub opposite the station!) and then I had to change at Cheltenham Spa as well.
Instead of getting home at about 9.45pm, I got home just after midnight .... ho, hum! Still, at least I did get home .... I'd hate to think what happened to people travelling beyond Cardiff!