It is a odd setup in Sunderland with the shared tracks to Heworth, I know I got caught out the other week when late night metro services got suspended, thankfully it was just before the GNE walkout, are they keeping the northside open once the building work has finished?
I don't know but am assuming that the northern (very scruffy) entrance will be tidied up and continue in use. There are stairs and a lift which it would seem to be counter-productive not to use for the Northern and Grand Central services - but perhaps someone could enlighten us on this.
The two tracks at Sunderland Station are BTW bi-directional. I have been on northbound Northern trains that have used the Southbound platform and Southbound Metro trains that have used the northbound platform. Some Grand Central services from London terminate in the Southbound platform before returning south. When the GC service is sitting in the Southbound platform waiting to depart, late running southbound Metro services usually by-pass it using the northbound platform (there is some confusion on the island platform when this happens!).
There is consequently an odd mix (possible unique in the UK) of Metro, Freight, National Rail (Northern, Grand Central and LNER on diversion) using these 2 tracks. I haven't seen Cross Country, Lumo or TPE trains, but they probably also run through Sunderland when diverted off the ECML.
Incidentally the Network Rail track is shared between Sunderland station and just before Pelaw (where the line from South Shields comes in and the erstwhile Leamside line also) - rather than Heworth. From Pelaw to Gateshead Stadium station there are 4 tracks with Metro and Network Rail services segregated before the Metro tracks dive down under Gateshead and Newcastle - emerging at Jesmond.
Following work done recently, the 2 track formation from Pelaw to between Jarrow and Bede Metro stations on the South Shields line is also now shared - previously where only 2 tracks were possible, one was for Network Rail and the other for both east and westbound Metro services.