Do you have a source for that production? Particularly one which makes it clear they did 5 tons a day for two full years?The New Haven Chemical Company was producing around 5 tons of refined saltpeter a day, or about 150 tons + per month , or 300,000 pounds, between June 1862- mid 1864. That's 3.6 million pounds in one year, or roughly 7.6 million pounds over the two year span where their production was the greatest. Mind you most of that 7.5 million pounds was going to Dupont, who was using this supply almost exclusively during that period. By that time Dupont was making about half of all gunpowder for the Army. And all of the British saltpeter wasn't being used to produce gunpowder for the Army. The Navy in particular was also stockpiling large amounts.
To be clear on this, though, 7.5 million pounds - if sustained - is 10% of imports from British possessions over the war.
Nitre beds take many months to mature (on the order of a year or two) and their productivity is limited. The ARW productivity of nitre was able to sustain combat leading to about 14,000 total British/Loyalist battle deaths over the eight years of the war, or about 2,000 a year; there are obvious difficulties scaling that up to a much more artillery-heavy combat which produced nearly 30,000 battle deaths a year over the last three years of the war.What would have happened? Probably the same thing that happened in the Revolutionary War, a booming industry in outhouse cleaning.