It depends where you get your info. People who don't read the comic or don't like it will make up anything. There's even those who say Snake Eyes can speak because of 1 lil mishap that occured in the comic (Scarlet 'dying' or something). Devils Due probably could have killed him off but here's the tricky part... Because GI Joe is a Hasbro property, they decide who is ok to kill off. Is there a list? Not really. But if you were to ask them specifically on characters, they could say YES or NO and compile a list from that.

For example, Chuckles, Flash, Mainframe, Daemon and Lady Jaye. Yet, they can be brought back in backstories or whatever. *shrug* DD coulda chanced offing old man Destro and had kiddy Destro take over. Which could have been more interesting in the scheme of things.