Gundam 0079 -> Zeta Gundam -> Char's Counterattack
-> the whole three series started with rivalry between Armuro and Char, they both die at the last film since one series isn't enough to end their journey
Zeta Gundam
-> Even though Camille, the protagonist doesn't die, this story still has a bad ending comparable to those who died. the protagonist fail to survive before the war even ends.
Idk if you want pure "dead" as the protagonist turned into corpse. But the Camille we knew is as Good as dead since his mind as been fucked up and destroyed by his enemy.
Even if he did recover as his mind finally able to talk and walk, the old Camille with his memories and personality is simply gone. It's pretty much replaced with someone new.
Mobile Suit Gundam: Iron-Blooded Orphans
-> The whole struggle of the Rebel against the government really show how strong is protagonist and it still shows the flaws of their methods too
The reckless protagonist died recklessly too.
Well, most Gundam have bittersweet ending and rarely bad ending where the MC is dead/something as worse happened.
But there's more bad ending than good ending in Gundam.