they are both immortal

Shaggy would eventually die, might take a couple thousand years but Kenny keeps coming back

Yes

There would be a tie.
Shaggy is very powerful, (in the meme lore) and he's immortal.
Kenny can revive when he dies, meaning he's also immortal, and if Shaggy used 100% of his power, Kenny would revive.
So I guess it's a tie!

wait till kenny uses 1% of his power

kenny’d outlast shaggy, he may die a couple thousand more times but he’ll come back, shaggy’d eventually die

Shaggy

Shaggy

Shaggy 👌💨

Shaggy have the ultra instinct with 2% of his power so.....Shaggy