You don't need to kill the tardigrade if all its food is already long dead.
It has certain implications relating to the odds of lower level life on other planets. Even if nothing is living on Mars today, it seems almost certain there's fossilized dead bodies up there. Possibly this is good news WRT soils and future cultivation.
It is good to try our best to sterilize our probes, because our relatively gentle launch and landing and relatively quick transit may enable a lot of things to survive the journey that otherwise couldn't. But there is a point where it stops mattering, because despite what you may think, Earth and Mars are already not fully isolated from each other, so sterilizing beyond that point doesn't change much.
One of the exotic possibilities for "how easy is life to start" is that it could still be very hard, but we could find life on Mars and perhaps even throughout the Solar System. But further examination might show that it all sourced from one location. (Which may or may not be Earth in the first place.) So there could be a period of excitement where it looks like life is really easy, only for it to turn out that the evidence remains a sample of one even so.
(The most likely way we'd make that determination is that there are certain choices in our biology that are extremely highly conserved, but at the same time, seem arbitrary. For instance, the mapping of what codons map to which amino acids. While there is some fiddling around the edges (as there are several more codons than there are amino acids), the core mappings are highly conserved. If Martian life is based on DNA and has the same core mappings, it probably comes from the same source as Earth life. Another example is protein handedness preferences, though that's stronger in the other direction; a biology with the other handedness would not come from the same source.)
It is also possible that life is, say, "medium" possible, and over the course of the Milky Way's life could be expected to arise a few dozen times and spread via panspermia, but in any given area only one of these may seed us, meaning that while there is variation in life, we can't witness it without traveling a long way.
Another possibility has been proposed that as our detection tools tend to assume DNA, and we look for DNA when "detecting life", that if there was some extremophile bacteria a couple of miles deep in the crust that truly was from another line of succession that didn't use DNA, or used it in a way unrecognizable to our equipment, that we could indeed even have run samples of such life through our labs and simply not know it.