Mello was too stubborn and cared more about proving a point than saving his and his friend's life.. L was dead at this point so he was ultimately trying to piss off Near. Right?
Death Note question. Why would Mello be upset over Matt's death if he knew It was coming, I mean, all he had to do was cancel the kidnap Takada plan.. Then voila! No dead Matty. xP?
Well, Rei Rei, you are right about the fact that he knew the plan was dangerous, you are right, he could have cancelled the plan and saved both of them because in the manga and anime, he knew it was dangerous. You're right tho, Mello is stubborn, he would be set on dying to one-up Near, even if it meant Matt's life too. He did not know Matt would die, he said "I never thought you'd be killed, I'm sorry..." Sort of a lie, he knew it was possible, but wanted to go on with the plan anyways... He had so much confidence, he couldn't see It failing! I think you've read too many fanfictions ;)
I was dead at that time, I cannot answer your question. I can tell you, Mello has always been stubborn so that was most likely it. He has always had a feud with Near.