Joey Paur, writing for GeekTyrant:
The latest issue of the Teenage Mutant Ninja Turtles (Issue #44) is the climax to an epic 4-part story called 'Attack on Technodrome' whereby Krang accelerates his plans to terraform Earth, a plan that will result in the eradication of all life on our planet. A surprise alliance results in a daring plan - and the stakes have never been higher.
TMNT is a Sci-Fi franchise, so it's entirely possible that IDW may eventually find a way to bring him back, just as DC did when they killed off Superman. But it's an incredibly bold move story-wise and will be interesting (and traumatic) to see the remaining three brothers dealing with such an incredible loss.
It goes without saying that this has a major spoiler warning, so only click the button if you want to know which of our beloved Turtles makes the ultimate sacrifice.