Holyhead drivers will just mean a slight natural wastage at Liverpool and Manchester; that is of course if you don't then use the same number of drivers overall by Liverpool doing their own extra trains.
I can't see Wolverhampton or Preston being at risk. Wolverhampton is where the trains come out in the morning and go to bed at night; Preston is the only logical changeover point between Scotland and London and of course with Blackpool.
I massively doubt the start of a Crewe depot for any drivers of Train Managers.
Drivers/Train Managers & onboard staff from Manchester and Liverpool and maybe Wolverhampton will get the chance to relocate to the new Crewe Traincrew depot by seniority, as
@driver_m has said quite a few drivers and some TMs live in the Crewe area. As well as North Wales work i'm sure some of the new Liverpool services and Euston will also be covered from Crewe.
Preston will probably stay as is for now but lose all Class 221 work, also Wolverhampton will lose all there Class 221 diagrams to Central Rivers and corresponding passenger services.
Depending on what new EMU & Bi-modes are going to be built and where the maintenance depot will be located will affect all these traincrew depots.