I was travelling about 3 hours into the disruption, and had been talking to Avanti on Twitter. As I was taking the bus I’d left around an hour, and it was just a case of getting off a stop earlier at Moor Street. I was planning on stopping at spoons for lunch, which was substituted for a meal deal, giving me the time to go via Chiltern.It's very lucky in that case you were in enough time to realise what was going on, walk to Moor Street, argue with the staff about the ticket gates, buy a new ticket, then cross to a train around half an hour before your intended one.
Was originally on the Avanti at around 14:20, arrived at Moor Street around 13:10 which gave me enough time to make the 13:43 to Marylebone, although this was just coincidental, and I agree lucky it gave me time to deal with the gateline staff.