On first glance it seems that this worm was brought back to life with scientific intervention exclusively. But with the disappearence of permafrost these worms will thaw on their own and will resume living and procreating. What I want to say is, that many species of these ice-aged worms may be alive already without anyone noticing, trough permafrost has been thawed away. Who knows what impact these worms will have on our recent fauna and flora?

This is kind of like time travel in a way. If one were to go back in time, you would mainly need to worry about the diseases and parasites you bring back with you. You are descended from those who learned to survive the diseases of the past so you are likely to have some resistance to it. You wouldn’t be perfectly safe of course, but not likely at more risk than if you stayed in your own time.

On the other hand, if you travel forward in time, like this nematode did, you are entering a realm that is full of virus, bacteria, and even fungus that have had decades to learn new tricks to survive that you would have no inherent resistance to.

The chance of there being some sleeping time bomb in the permafrost seems low to me since everything alive today is descended from those who survived that germ or parasite in the past.