If i got the gastric sleeve my concern is long term. for instance, what would happen if i got cancer in the small amount of stomach that i have left?

It's no different: than if you get gastric cancer anywhere in your stomach without the surgery. Any cancer needs to be diagnosed and treated quickly and appropriately. Talk w/your doctor if you have concerns.

Same treatment: The treatment would be the same, but you would likely need all of the remaining stomach removed if you were to develop cancer. Sometimes a total gastrectomy is needed even if you still have a full size stomach at the time of cancer diagnosis. To replace the stomach, part of the small intestine is pulled up to where the stomach used to be so that food can be digested.