Quick A: Yes, as any other virtual member function.
Recently on SO:
May a C++ destructor be declared as final?
And if so, does that prevent declaration of a derived class:
Yes, because the derived class would have to declare a destructor (either explicitly by you or implicitly by the compiler), and that destructor would be overriding a function declared final, which is ill-formed.
The rule is [class.virtual]/4:
If a virtual function f in some class B is marked with the virt-specifier final and in a class D derived from B a function D::f overrides B::f, the program is ill-formed.
It's the derivation itself that is ill-formed, it doesn't have to be used.
Is declaring a destructor to be final a workable idiom for indicating that a class is not intended to be used as a base class?
Effectively, but you should just mark the class final. It's quite a bit more explicit.