Asbestos Roof Question

[Curran D Bishop]

I'm considering a deal that has an asbestos roof that was put in in 1900. It's still in good condition, but I'm seeing estimates that asbestos roofs are good for "50 years or more"; I had a friend with one that he called a "100 year roof"; that's great, but this roof is 120 years old... 

At some point it's going to have to be replaced, is there any way of estimating that?

And what that looks like: do people just roof over them, or is some other step required? And is that having the EPA come in hazmat suits? I saw a comment somewhere that asbestos roofing was less hazardous than siding and was generally just removed like old roofing...