There's no obvious customer to sell them to - conversion back would be expensive (if even possible) - the USAF as additional E-11 airframes may have been one, but they are ordering new (and only the first E-11 had the Sentinel-style add-ons from a previous role)
Replacement? Well there's the NATO AGS system (Could the UK buy into that?), P-8 with AGS (are the USN going ahead with that?) Or your and my favourite, the 'capability gap'