I mean... wasn't it pretty obvious that Danno never had any intention of surviving past his revenge? I wouldn't be entirely surprised if his whole amnesia thing is at least partly an attempt to push Tatsu away and save him from the aftermath.
(Comment below) Yeah, it's obvious, but I think Ryuzaki is quite naive when it comes to Danno, or he simply pushed the truth to the back of his mind. It's normal.