No, is the most obvious answer there is. Atleast not his own death, but others and colleteral damage.
He got his chest blown out, what do you expect? And the "please" was not an attempt to make Sentinel spare his life. It was an attempt to make Sentinel overthink his plans to enslave the human race. And in all honesty, that was a great little character moment for Optimus and Sentinel there.
How about you kill 5 cons rip one's arm off then someone sneeks up behind you stabs you in the heart then shoots you and you'd shout "No!!!!"too
Optimus begging Sentinel for mercy only to headshot him 20 seconds later left me feeling rather cold.
He says "Please!" while Sentinel is raking his ragged body across the bridge and kicking him around; you can take that as either a.) pleading for Sentinel to spare his (Optimus') life ("Please, don't kill me, Sentinel!") or b.) attempting to appeal to Sentinel's better side ("Please, Sentinel! Don't do this! Don't enslave the humans! You're better than this! Remember, you're an Autobot!"), which most people seem to gravitate towards the latter. He's not really screaming for mercy, he's attempting to just flat out stop Sentinel from doing what he's doing. Think of the scene. Sentinel is about to kill Optimus, but is interrupted from completing said act. Optimus kills Sentinel because, well, Optimus wasn't interrupted. They both had the same intention when they engaged each other in Chicago to stop (read: KILL) each other, it's just that circumstances dictated that Optimus succeeded in his mission. If Optimus had said "I'm not going to kill you, Sentinel!" and then killed him, that would've been more strange. But Optimus didn't betray his motives. He was fully intent on stopping Sentinel, no matter the cost. And Sentinel was willing to do the same to Optimus. One succeeded, the other didn't.
Optimus doesn't want the villain to kill him, because then he won't be around to stop the villain later. He was fine with dying with Megatron/Sentinel, or if his death would somehow thwart their plans. He was perfectly ok with suicide by Allspark because it would deny Megatron the ability to make a new army, and the other Autobots and human military combined could probably finish off Megatron, but not Megatron killing him in the forest because then nobody would stand between him and Sam, and not Sentinel killing him, because the other Autobots wouldn't be able to stop him retriggering the pillar. Ironically in the later cases he was actually wrong, as the other Autobots did arrive in the nick of time to stop Megatron getting Sam, and the other Autobots destroyed the pillar, meaning even if Sentinel killed them all afterwards his plan to bring Cybertron to earth would still have been stopped.
I don't buy that. He had plenty of time to say that during their fight on the bridge. Optimus was clearly in a rage and trying to slice his damn head off. Only when he was knocked down did he start "pleading".
Haha, obviously. Optimus may be an emotionally strong leader, both as a mentor, and a military leader, but he fears death like any regular soldier does. He experienced so much death back on his planet, he probably fears it more than any human does. But, he clearly knows what the consequences of Decepticon victory will be, and is willing to sacrifice everything for it. Optimus' morals stand above his fears and disabilities.
Actually before Optimus' right arm was cut off, Sentinel was giving a speech where he was saying,"...the bravest of us all..." but "unable to make the hard decisions..." I noticed when Sentinel was saying the second statement, Optimus actually had one of his swords at the former's neck but seems unwillingly to finish his mentor.