The unique thing that can kill a tartigrade is the explosion of an supernova, I think (very good video and song by the way)

good
but i think death should just give them some kind of sickness and then they die

Yeah death can't do much to a tardigrade.... except wait half a year. Average lifespan of an unfrozen water bear is about 4-6 months. While they are pretty much indestructible and can be found in some of the most unlikely places.
Besides all that, they are astounding creatures, for reasons even beyond their unbelievable immunities. All that being said, infectious song and great animation. Good job!

Tardigrades are awesome!

Goes on a bit long, but this needed to exist!