Hi Lyuba,
You're using a third conditional here, which is about as far as you can backshift a conditional phrase anyway. The phrase is absolutely fine as far as I can see.
The "had said" part is actually past perfect which, as far as I've looked, is not actually part of indirect speech. Even so, if the phrase began, "He said...", you would still keep the third conditional structure.
If the conditional structure changes, then the possibility of the result changes dramatically.