For Winners / Marshalls, I think at some point having 2 separate administrative functions for the 2 stores will cause them to merge the two.
True, that TJX brought Marshalls to Canada side-by-side with Winners, rather than being the result of a takeover, but they can always rethink the decision.
Historically, a lot of stores have eventually merged:
Hudson's Bay's take over of Simpsons
Sears decision to run eatons separately
Best Buy's takeover of Future Shop
Rona's takeover of Lowe's
SportChek's trakeover of Atmosphere (formerly Coast Mountain Sports) seems to have them co-locate
Pattison changed its PriceSmart concept from being side-by-side with Save-on-Foods to being an Asian brand, and they also eliminated a lot of their others lesser known stores - Overwaitea, Cooper's Foods (bought in 1999, merged in 2016), etc.
https://canadiangrocer.com/coopers-foods-banner-disappear-bc
https://canadiangrocer.com/overwaitea-converts-six-stores-save-banner
Then there is Chapters (large stores), Indigo (lifestyle stores) and Coles (smaller stores) which seem to co-exist but I doubt you'd see them side-by-side.