I would agree IF Northern had no new rolling stock incoming. However the introduction of the 195s and 331s will change the equation and the 150s & 156s will look even more dated. I believe even Northern have stated that once the new trains are in service (logically passenger numbers increase as many in the North have long been put off using trains by the dilapidated state of Northern's diesel fleet) attention will quickly turn to what to do with the 150s & 156s and how to modernise/replace that fleet to encourage additional passenger growth. I can certainly see 50%-75% of the 150s/156s being replaced as part of new order when the new Northern franchise is awarded in 2025/27, however the problem is whether they would need to be bi-mode given a potential ban on diesel trains during their 30-35 year lifetime in service. I generally agree that losing the 170s/185s to Ireland (temporarily anyway) wouldn't be a disaster.