Following a rumour that Saturday 15th February would be the "last day", I have had the following from a manager within Northern:
142's will be running until "at least" the 6th March in the North West, there will still be 2 diagrams that will include a 142 on them. There is already a nominated pool of 4 that will work these, with the other 10 NH based units moving to HT from the 15th Feb onward for storage.
Hopefully it's of some use to people trying to get as much last-minute mileage as possible!