Coleman's is going to survive here. People are far too nationalist to let our own go under.
Beyond that... I can definitely see CostCo wiping out the rest. If Walmart builds a proper grocery here, it'll do very well among the same suburban families as well.
Downtown will always be small places like Water Street Variety (which brings in its fresh and baked goods from Bidgood's Grocery, another local favourite based in Goulds), Belbin's Grocery, etc. In every way, downtown residents prefer one-off local shops to chains. We don't even have a McD's downtown.
The edges of downtown have a regular Sobeys and a massive Dominion (in the former Memorial Stadium). Both are well-used by the surrounding neighbourhoods so I don't think we'll see them close down. That said, there is a Coleman's that's very close to the Sobey's - so Sobey's may want to back out of the downtown a little farther. We'll see.
There's one other 24-hour Dominion (on Blackmarsh) that's relatively close to downtown. It's always packed. I don't think it'll go anywhere.
I'm sure I'm forgetting a bunch.
*****
Sad thing is Safeway is famous for treating its employees exceptionally well. It has a near CostCo-level reputation. I'm sure that's all going downhill now...
Also, their chicken pesto deli sandwiches... OMG... their delis offer a fraction of what Sobey's does, but it's all awesome.