What happens in the final stages of crohn's?

Not clear: On what you mean by "final stages" need to be more specific in order to assist with this question.

There is no final ..: No final page per se, with the array of new drugs, and surgery, most patients will do very well. Enbrel, humira, remicade, (infliximab) and more conventional drugs, either alone, or in combination, can control most patients, without need for surgery!

Crohn's disease: If you mean nutrition, antibiotics, all medications& surgery are used& nothing left then you can call it final stage. Then prognosis is poor. There are no stages of disease going from one to an other. No cure for cd. It flares and calm down. The fistula, obstruction& colon cancer happen. The course of the disease& response of each person is different. Some stays in remission for years than others.