Ok, first of all make sure you are talking about the Y-Pipe. If it is not busted now it won't "just break." Generally it is a result of lack of support when removing the Mufflers. Some folks in trying to get the mufflers on smack em with a rubber mallet. That places pressure on the Y-Pipe and messes it up.
A cracked Y-Pipe requires the replacement of the Y only not the entire system. Cost is around $170.
A cracked Y-Pipe is covered both under original warranty and extended.
Replacing the system with duals would eliminate the potential problem.
If you have no problem now, don't worry about it. If you ever remove the mufflers just be careful.