In my long life, even before legal adulthood, I almost never went into the woods without being armed, and now I rarely go anywhere in public unarmed.
I guarantee that they can be killed. Men have killed even blue whales on an industrial scale. Any of the rifles I regularly go afield with can easily kill a sasquatch, even if it escapes wounded to die later. I'm quite literally gunned for bears.......BIG bears........because I live in an area known for big bears.
That written, and even though I formerly thought that killing a sasquatch for the advancement of science was valid, I no longer believe that a sasquatch should be intentionally killed. However, just one bluff charge or stalking event, and if I get a shot, I'll punch a hole through one with no regrets whatsoever, and I'd have no problem leaving it right where it falls for its kin to drag away or for the birds to feed on.