I don't think the PoD is sufficient to take Quebec.
The goals in that particular battle were for Montgomery and Arnold to meet up in the lower part of the city and scale the walls after clearing it out, but unfortunately they could only do this under the cover of a snowstorm otherwise the British could mop them up from the walls. Arnold was injured in his push- not unsurprisingly as they were fighting in unfamiliar terrain, and iotl yes Montgomery was killed. The Americans were still completely outnumbered in the battle and it was pretty poorly planned. Had Montgomery simply been wounded it would of course change the war, but in the battle in and of itself, him surviving is a thing of luck and I highly doubt even if they'd manage to get a foothold in the city they'd be able to make their way up the walls to the upper city- it'd be sheer suicide.
Now long-term, had they both survived and failed scaling the walls (but taken the lower city), they might have a much better idea of Quebec's logistics and perhaps be able to keep a few spies and contacts to find a more opportune time to attempt to take the city That in and of itself imo is a more realistic and intriguing PoD.