I'm guessing they might get them - flog off the D's in part exchange but 18 at the very best, maybe less.
Having spoken to Boeing and the British Army on this very subject, the most likely scenario is that an undisclosed number of the 66 Ds would be 'remanufactured' to Es (new airframes, but with the old engines, MTADS/PNVS, fire control system etc). How many has yet to be determined (or at least announced).
It's win-win really, as you're essentially getting new aircraft but at a significant fraction of the cost (the expense is primarily locked up in the parts and systems you're cross-decking)