Depends! I'd walk/cycle/wait/bus depending on the circumstances!
I saw a train from Burnley Central to Colne was cancelled, so I cycled from Burnley instead of Colne. Not quite the same thing, but the same principle. I was cycling to Skipton anyway and certainly didn't want to sit around at Burnley Central for an hour! It just meant the ride was a bit longer than I'd planned.
On another occasion there were too many bikes for a train to Snaith (which has very few trains!), but the Guard asked everyone for their destination, those of us for Snaith were given priority and those for places like Knottingley had to wait.
I was unable to board a train at Porthmadog heading towards Pwllheli. We were actually wanting to go to Barmouth, but were going via Pwllheli rather than hang around. The Guard wouldn't let us board because it was too full (an unfolded pushchair was allowed to board though) and we didn't want to hang around for ages and risk not getting on the train to Barmouth. So we cycled to Barmouth from Porthmadog.
I was unable to board one of the last trains from Man Vic to Castleton because it was too full, so was unable to get a lift I'd arranged with
crossover from Castleton to Huddersfield, I ran to Man Picc, and got TPE from there. My ticket was routed via Hebden Bridge but no-one appeared to charge an excess, so it didn't cost me any extra.