Board Thread:Naruto Discussions/@comment-28846843-20160625201600/@comment-9782468-20160701220745

They're is most certainly a chance that his most powerful technique would now take all his chakra.

Hiruzen's reserves were hella low when he died. I mean, the dude was 69 years old, and he hadn't been battle tested in so long. He must have had some techniques that were beyond him at that point.