Entered into Rest

What if Shredder had Baxter Stockman create a highly distilled, more potent form of Karai's venom that kills within an hour of administering? What if Shredder planned to inject this venom into one of the turtles in order to draw Hamato Yoshi out of hiding? What if he succeeds? Splinter and his sons are eager to avenge their dead sibling. But...is he really gone?