The villain contacted DC beforehand 

He told him if DC didn't give up his immortality he'd kill the states and the main five 

So DC went alone 

When they met, DC ordered him if he were to give up his own life, he'd leave the others alone

DC faced death with dignity, as only the American Gov could 

The others caught on too late to what DC was going

Did

Did DC leave an explanation of what he was doing

"Your lives are in danger, I can't live with myself if I put you all in harms way. I'm the American Government, I'm supposed to look after you all. I love you, more then words can ever say." 

HELEFTHISFLAGPIN

WHOUNDTHISANDWHYWASITNEWYORK

Texas rounded the corner with the others just as the gun went off 

Florida saw the moment DC hit the ground

Also I like the idea that the villain uses DC's immortality against the main five like, to shape shift into him so they won't fight them

"DC": Oh go ahead Florida, cry. Remember? 'No one likes you?' Remember how you drove him to the brink of a breakdown? 

"DC": You act like you're so 'high and mighty' Loui, when did you back up DC? When did you help him? Oh right, you were too busy acting like second Florida.

"DC": The high and mighty California is going to lecture me? Hey, how many times did you jump down DC's throat over something he was just the messenger for? 

"DC": 'Is it time to boogaloo?' 'The south will rise again?' Tell me Texas, how is it simultaneously dating a fed and wanting the government gone at the same time? 

"DC": New York you never liked being involved in the meetings, don't even kid yourself. If those meetings went away today you'd give less of a shit, wouldn't you? 

Anyway I should get some sleep tonight, huh?