Keel integrity on older offshore sailboats is a subject filled with ambiguity. That said, we need to really think about this when selecting a new boat since keel dropping off is not something we can realistically ameliorate, or probably even survive.
On the bright side, if we avoid certain construction methods, as far as I can see the chances of the keel dropping off, at least without warning seem to be pretty small; although, of course, like most things around offshore sailing we have no reliable statistics to prove that assertion.
So what to do? Let's start off with what I'm reasonably sure about, and then move on to the higher ambiguity stuff.