Well, “tend to zero” is not the same as “goes to zero”, Tend to zero is going to zero without never reaching it. I think we’re on the same page here.
What mises is saying is that it tends to some unknown number, which may be 5%. But not that it gets smaller and smaller arbitrarily close to zero. That is not the case. There is some lower bound greater than zero. And of course, that number changes with time, since it comes from people’s minds.
These posts may help: