It seems clear that any more complete theory describing particle physics must inevitably reduce to something equivalent to the standard model in the appropriate limits. So in that sense, the standard model will hold forever.
It's exactly the same as saying that Newton's law of gravity will hold forever. It applies very accurately under most circumstances; situations that require us to deal with the complexities of general relativity are quite rare. (GR only begins to differ from Newton's gravity when you have extremely strong gravity or when you need extremely high precision.)
But if you want to really understand the inner workings of the universe, Newtonian gravity won't cut it: you need GR. And it's pretty well established that the standard model can't be the whole story, either: its mathematics eventually break down when the energies get high enough. So there's got to be something else up there... we just aren't sure what it is.
It's exactly the same as saying that Newton's law of gravity will hold forever. It applies very accurately under most circumstances; situations that require us to deal with the complexities of general relativity are quite rare. (GR only begins to differ from Newton's gravity when you have extremely strong gravity or when you need extremely high precision.)
But if you want to really understand the inner workings of the universe, Newtonian gravity won't cut it: you need GR. And it's pretty well established that the standard model can't be the whole story, either: its mathematics eventually break down when the energies get high enough. So there's got to be something else up there... we just aren't sure what it is.