I would like to think I'm a good enough employee that all being well I won't need to leave the railway (I have fairly extensive customer service, management and operational experience both in and out of the industry and I believe I'm held in pretty good regard) but I really don't need the stress.
It will likely happen though but you sound well placed to deal with it. I have a great deal of sympathy for Southern staff but very little for Merseyrail (apart from them favouring people who don't strike for trainee driver jobs). It seems like the transition will be long and all effort will be made to avoid compulsory redundancies.