I'm not seeing any evidence the 11th Arm Div, or XXX Corps tried very hard to advance north into the Antwwerp suburbs. Post War Horrocks opined that it was a mistake not to have done so, before his Corps was withdrawn and moved east for Op MARKET-GARDEN.
As to the 15th Army collapsing after being cut off; it depends on what food and ammunition were stockpiled in the coastal forts protecting the Scheldt, or what they could bring with them in the rout from Flanders.
A few alternates:
XXX Corps hooks back west & a division seizes Brugge, a road hub, thus creating a second pocket as was trapped at Mons. This delays the capture of Antwerps port by a couple days, but prevents any appreciable size force of retreating to and across the Scheldt. So, the area has only a few caretakers and the men manning a few coastal artillery batteries.
A couple divisions of Brownings Airborne Army seize the north bank ferry crossings of Walchern island, Beveland, and the neck. Perhaps the airport at Brugge as well. This also makes a retreat of 15th Army problematic. Its probably rolled up by the Canadians in Flanders.
Anyone of these requires a huge amount of foresight and focus by both 21 Army Group and the army/corps commanders.