On the night of Storm Daniel in September 2023, the Caledonian Sleeper's Highlander arrived at Edinburgh Waverley four and a half hours late. The Fort William portion was cancelled and the passengers provided with taxis for a journey of about 150 miles. I believe that was not the only occasion when this has happened.
Certainly isn't!
I arrived into Edinburgh over five hours late in September 2024 and around 25 of us were then taxied to Fort William.
Black cabs too, or at least, mine was. The driver absolutely loved it. A decent, guaranteed fare, no hassle from passengers and obviously fantastic scenery. I chivalrously did the other passengers a favour in telling the driver as he was about to turn round outside Wetherspoons in Fort William that he didn't need to and I was more than happy to get out there!

They were a seemingly rather affluent group who were paying the driver cash in hand (I presume) to take them further.
Furthest one I know of was in a similar area. I had a Replacement taxi Fort William-Bridge of Orchy in a (not so) wild goose chase to catch the Sleeper after the ScotRail was delayed and they kindly let the Sleeper leave. Talking to the driver and he said the furthest rail job he'd ever done was Fort William-Cambridge, and once had an insurance job for medical grounds Fort William-Weymouth. All ran on the meter too.