Somehow, I highly doubt that the USN would replace it's Hawkeyes with a helo-type. The E-2C has significant advantages of speed, range, ceiling, crew size and facilities, avionic space, and a larger, more powerful antenna than any previous or proposed vertical take-off aircraft.
Of these, maximum ceiling is most vital, as the maximum sensor coverage, and range of the antenna is limited by LOS. ( IE. the curvature of the earth. )
Naturally, the E-2C operating at it's nominal mission altitude in excess of 10,000m would be much less limited than a Seaking, or Merlin in this regard.
In addition, the very high operational altitudes provides an AEW&C aircraft with much longer endurance/range, and an increased measure of protection from some air defences.
For a smaller STOV/L vessel, such a helo AEW/C4ISTAR platform may be sufficient, or even ideal- but if you have the advantage of an enormous flight deck such as those of the USN's fleet carriers, then it is probably better to use that space to launch and recover larger, more capable platforms.
Alternatively, I suppose it could also be used to carry large numbers of AEW&C4ISTAR UAV's- that when operating in networked group could function as well, or perhaps even exceed the performance of an E-2C.
Of course, they may not be as well suited for some other roles that could be performed by a larger, multi-role platform.
Perhaps a mix should be considered.
But I don't want to digress much farther from this thread's topic.
I have often wondered whether the missons of E-2, C-2, and to some extent the Viking might be replaced by varients of the C-27J, CN-235, or CN-239 airframes.
Additionally, such an aircraft might also be able to provide the USN with a carrier-based reconniassance, and surveilance capability similat to that of the EP-3, and the RC-135.
Finally, the greater size and range of these large fixed-wing types
may prove useful as a special operations, and gunship platform for amphibious, and/or US SOCOM operations.
At first glance they seem rather large, but then again I'm sure nearly everyone has seen pictures of the Hercules that had recovered, and launched from a USN CV during the Viet Nam conflict.
It is possible. The question is, is it affordable, or really even necessary to replace the Hawkeyes at this time?