Not so tough after all.
....a living tardigrade that's not in the cryptobiotic state is actually pretty fragile.
If you stuck a living, active tardigrade directly into liquid nitrogen, boiling water, your own stomach acid, etc. etc., you'd kill it instantly.
Your own immune defenses would make short work of any tardigrade that got into your bloodstream.
Tardigrades can get attacked by viruses and bacteria and fungi and predatory nematodes, and they can be physically damaged as well.
There are lots of things that can kill them.