S. Korea already has four E-7, & is looking to buy four more AEW aircraft - with E-7 being shortlisted.,
Last I heard, E-7 was top of the NATO list of possible replacements for E-3, & I doubt NATO Europe members will write off the E-7 if the USA drops it. It's well proven already.
The most likely alternative is GlobalEye, already chosen by Sweden & France, but then E-7 is already in service in Turkey & about to enter service in the UK. There are 14 E-7 in service, three 737s being modified for the UK with possibly two more wanted, orders for 10 more being considered by NATO & S. Korea, Canada & Saudi Arabia (5 E-3) looking for new AEW aircraft, & at some point, probably Japan (4 E-767). Not counting the USA, that's 17 in service or production, & possibly more than 20 more sales.