Well, that answers that question, the two being diverted to Saudi are not being replaced by more orders. The T45 order is being capped at 6 - a 25% reduction.
The Times: .....The defence budget also contains provision for six Royal Navy destroyers worth £3.6 billion. BAE and VT, which are building the destroyers, have launched two of the ships already and began work on the remaining four without a fixed contract. However, a proposal to build a further two of the Type 45 destroyers has been axed from the MoD budget.