There is a Tamil proverb "Aarilum saavu noorilum saavu" i.e. death is certain at 100 or 6. Many interpreted this w.r.t years of human life but it actually represents karn. If he had joined pandavas and became kuntiyas also he could have died and as he remained with kauravas as 100+1 also he might have died.
But as we knew about duryodhanan, he might have fought with karn also 😉