I'm gonna go ahead and guess he turns into some manner of giant mantis-man. Sheldon has often been physically compared to a praying mantis, after all. Or MAYBE he'll turn into a giant mantis-man wearing a Flash costume. That'd probably be cool.
they haven't decided yet but Sheldon I believed threatened to get on a train and "live off the land" which is a way of removing a character with out actually removing them all together if and actor wants a break, similar to going to prison in some soaps