Board Thread:Naruto Discussions/@comment-3297904-20150325023132/@comment-1018594-20150325041122

Sarutobii2 wrote: If he told Hiruzen the truth, there'd be a risk of the news being leaked to the Uchiha clan or if he returned back to his clan with a missing eye, they probably would of assumed Konoha was behind it and immediately provoke them into rebelling against the village. His death was necessary to temporally protect both the village and the Uchiha.

Pretty much. And even if Shisui survived long enough to tell the Konoha higher-ups, Danzo would have had him eliminated soon after anyway.