The shops are never going to reopen.
The works at Queen Street consist of railway works and then the general redevelopment of the non-railway area. The tunnel works are not actually related to electrification, since the necessary clearances already exist for the overhead wires, but as the concrete track slab is decaying they have decided to do the works now rather than having to do them once the station is even busier.
Another component of the railway works is that platforms 2, 3, 4 and 5 need to be extended so that 8 car trains can be used on the line. Since the tunnel is at the other end, the only way to do this is to extend them into the concourse area. They will be extended far enough that the entire front of the station absolutely must be rebuilt, as the space currently used by the shops and eateries will be the concourse. It isn't just the front of the station being rebuilt either. In essence, there will be nothing left of the station building other than the original Victorian train shed roof. You can look at the new concourse layout in this
PDF from the EGIP website. If you go to
this link and scroll down to the bottom to the Project Gallery, there are a variety of plans available to view. Click on the thumbnail (there are several pages of them) and then 'Download PDF'.
In the PDF I linked to directly the station redevelopment works are highlighted in yellow. The dark yellow area is the area within the ticket barriers. All of the current shops are gone completely, and are meant to replaced by shops in the Buchanan Galleries extension to the east over the current car park. As the BG project has been put off, it is still unknown exactly what will happen once the new station reopens.