There is no point in keeping it past Hemel, as next passing point (Tring) would require another circuit, thus not saving the required units.Bourne End is not in their route knowledge. Merely the platform spin at Hemel. Hopefully when Watford north is recommissioned they’ll keep the Hemel at least.
You were lucky to keep Hemel, it took a lot to persuade DfT to allow you to keep it. The only way we could persuade them was because it was “free” and the performance risk twice a day was worth the benefit it brought if for whatever reason Watford Bay was blocked.