Cor Blimey
It used to be a standard question on line checks, "How is your range affected by gear down?" and you would get out the tables and do a calculation - there is a huge difference - basics.
More basics is to do a fuel check every now and again - so even supposing the decision to continue had been made - the high consumption should have been picked up on route.
Other reasons for avoiding long flights with gear down include lousy 1 eng performance and service ceiling.
Then you bust it and you are a hero. Sorry but it wouldn't have acheived even a marginal pass in a sim ride.