The back corner (NW corner) wasn't "dead" until the entrances through the TD Bank branch and the breezeway were closed. They were still open in the early 1990s from what I recall (From TD Tower you could walk through the bank, across the breezeway into Eaton's and get to Robson street without stepping outside).
The new 725 Granville office lobby will reinvigorate that breezeway, but the connectivity from the bank through to the department store will still be lost.
************
Pics by me last night -
I'm not sure what the steel structure is for - it doesn't look like it will be hoisted up, as they've installed steel studs in the area (but I guess it could be?). It could just be a raised floor in that area (as a transition from the entrance mezzanine), which might create the need for handicapped ramps, etc. The steel does not extend to the rotunda entrance (where the entrance mezzanine would be).
Looking towards rotunda:
Note the cove ceiling above the raised area:
A bit farther south (south of the emergency stair stack), the whole ceiling is uniformly lower:
Pics by me today:
The concrete for the raised sidewalk extension was poured yesterday:
You can see the planters along the stationhouse and the angled floor where the steps will be installed: