I think this might be a useful language feature and was wondering if any languages already support it.

The idea is if you have:

class C
  virtual F
     statement1
     statement2

and

class D inherits C
  override F
     statement1
     statement2
     C.F()

There would be a keyword applied to C.F() such that removing the last line of code above would cause a compiler error because it's saying "This method can be overridden but the implementation here needs to run no matter what".