A lot of people may bitch about how Ironhide died, but this is actually a good example of how dangerous Ironhide really was - Sentinel was too scared to fight him face-to-face so he had to shoot him in the back to avoid taking too much damage. The only reason he killed Ironhide like this is because he perceived him as the biggest threat next to Optimus, which is pretty much true.
Shepherd: For the sake of our country a deal had to be made.. with Makarov! shoots roach Ghosts: What.. have.. you done.. ahh Shepherd: I hearby discharge you from duty.
Ironhide's last words are what make this scene sad because when he said "what have you done", it was that moment he realized that Sentinel had planned something bad (Chicago) and when he screamed "Nooo" Ironhide knew that he wouldn't able to stop it
I feel like Ironhide is flipping sentinel off 1:14 if you noticed, his fingers excluding the one finger and curling before they fall apart and the one finger is sticking up and was the last to decay