What amount sugar would one have to consume to fall into a coma?

Depends on pancreas: A normal weight person with a normal pancreas can go on consuming high amounts of sugar for many years ( many do) and it can take years for a normal pancreas and its secreted insulin to develop resistance over time. That said, a type one diabetes patient, with No insulin secretion, could fall into a coma if deprived of insulin and ate several high sugar meals within a day.