After they went mad, Kyle had tea parties and Dan hid up in the trees though his location hasn't always been able to be pinned down to a proper timeline.
After they went mad, Dan wasn't Dan and Kyle wasn't Kyle. But then that brings the question; who are they now? Dan's Dan and Kyle's Kyle. Sometimes.
After they went mad, only some parts of them were there. Dan could still sing but he used his voice to trick people into going into his maze. The maze that had no exit. Kyle called out for Dan randomly at night, then got confused because he knew no 'Dan'
When they went mad, Dan forgot Kyle and Kyle didn't forget Dan.