So Runcorn loses its through trains to everywhere south of Crewe? And its fast trains to Liverpool?
As notlob commented, there would still be scope for fairly good services to Runcorn using released WCML capacity. Here would be my ideal world suggestions for Runcorn.
In addition to any Merseyrail stopping service running through from Edge Hill onto the present-day Northern Line (perhaps 2 TPH continuing to Chester via the Halton Curve, 2 TPH on to Crewe), there could still be
(on a 1 TPH each basis)
a. something like today's Liverpool-Brum service (in addition to faster services via HS2)
b. a Lime St High Level-Manchester Airport-Piccaddilly, via a western link ti the preeent airport station (a hell of a lot more use than a high speed station in a field a couple of miles away)
c. a Lime Street-Crewe-Derby-Nottingham-East Anglia service (taking advantage of reduced conflicts at Crewe) to replace the present day Liverpool-Norwich (which would be diverted to 'NPR' and probably sent to Hull after Sheffield)
d. whatever longer distance services are being sent via the Halton Curve - hopefully, hourly trains to the Marches and south Wales.
Runcorn would struggle to justify direct London services if HS2 served Warrington Bank Quay twice hourly and took over as a railhead for the area, but would apart from that have much more frequent and diverse services. Easy connections would be maintained to Crewe and via an enhanced, electrified Manchester-Chester service, through Runcorn East and an interchange station at Beechwood, and perhaps with fast buses feeding off its busways to get people from the town itself to Warrington.
In other words, properly designed as part of an enhanced network generally, a Liverpool high speed line could bring benefits to a lot of other places too