hello today during the strike day i travelled to warrington from chester but on the way back due to strikes and a delayed train i caught the avanti to crewe and then crewe to chester. while i wasnt pulled up on it or ticketed, i would like to know if this was a valid route and could be a valid route in the future. thanks. it was an anytime day return
It isn't normally permitted, but if you would have been stranded then Avanti (or any other operator that could assist) would be obliged to help you out by accepting your ticket, for example.
If you weren't going to be stranded but would have been delayed by more than an hour, you could require the operator at fault to re-route you at the earliest opportunity, which essentially means they should arrange ticket acceptance or whatever else is necessary to allow you to travel by the fastest available route in the circumstances.
If you would have been delayed by an hour or less, you could have been required to pay an excess for travelling via a non-permitted route. This would have been the difference between the fare paid and the cheapest ticket permitting travel via Crewe; since there isn't a through fare from Warrington that permits this, arguably split fares from Warrington to Crewe and Crewe to Chester should be used as the basis of comparison. But it's somewhat of a grey area.
In any event you could claim Delay Repay if sufficiently delayed (15+ mins if Avanti, Northern, TfW etc. are responsible).