Chaos is not beatable, they are abstract concepts that take form in the physical universe and their own realm, which is the psyche of all living things.
For chaos to exist in Marvel you would have to connect the souls of the setting to Chaos itself, or else it literally doesn't work as intended, in which case the argument is pointless as its no longer proper chaos.
Understanding that, should Chaos be implemented, the Marvel Universe is fucked.
Fighting Khorne, the very act of fighting against Khorne, fuck it fighting period, sustains him and makes his existence absolute. Khorne, the chaotic entity, cannot be defeated through any kind of war fare as that concept IS him.
You can say "but ____ beat death, but ____ conquered universes, but ______ killed gods" and that is all as well, but Khorne is NOT a God, he is called it but from the perspective lore Khorne, and the other "chaos gods" are representations of all life. Khorne is war, combat, hatred, the whole deal. Fighting him doesnt work by his very nature. At best your going to be lost in the struggle and work for him, Hell one of his greatest champions is a deamon hell bent on killing him, as the action alone fuels the War god.
Even with the others its a huge maybe, Slannesh is the most likely to be beatable, since he plays upon emotions and is the weakest, but any being with a shred of mortality will be his/hers/its forever simply by looking upon it. .
Nurgle could be beaten back, but he represents the cycle of death and life, wiping him out involves ending the cycle entirely, probably not a "win condition" for marvel heroes.
Tzeentch, by his definition, can never be beaten unless he wants to be. He is magic incarnate. Yeah, all those crazy magic characters... fuck it they wield the pieces of his very staff with their spells. He has plans that always could ensure he wins, by his nature. Hell he could win the 40k setting immediately with a plan he has, but doing so would remove any more needs for plans.