Anything that that backs up
1 ) your assertion that the UK was only relying on Loyalist support
2 ) your assertion that said support would never be adequate
3 ) your assertion that the UK was blind to said inadequacy
4 ) your assertion that those involved with the Vermont negotiations were deluded
The negotiations between Haldimand and the supposed "Vermont separatists" (which seems much more accurate in this case than "Loyalists") began in 1779-80, which was, after all, three years after Saratoga and two years after French entry into the war, which means that Haldimand et al are considering trying to sustain a separatist state south of the border after losing an entire British army in the same theater and at a time during the war where the possibility of a French combined arms expedition landing somewhere between Nova Scotia and Georgia.
So:
1. Haldimand had (IIRC) 3,000 British regulars and 4,000 German mercenaries to defend essentially everything from Quebec to Montreal, and operate in support of the supposed Vermont separatists; by definition, given the results of Saratoga, the separatists (supposed Loyalists) would have to defend themselves against the Americans, not the British;
2. Saratoga would seem to answer the question re Loyalists in Vermont and northern New York;
3. Again, after Saratoga, expending any British resources in the northern theater beyond simply defending the Canadas seems rather blind;
4. The British in the northern theater had literally just seen a British army surrender in the field to the Americans; seems rather delusional to expect a second offensive in the same theater was particularly thoughtful strategy.
Best,