Plus NBC would have to run WCVB as an ABC affiliate for 2 years, as their agreement with ABC doesn't end until December 2018 defeating the purpose of pulling their affiliation from WHDH.
If NBC leaves WHDH, the only options they have are 1) Subchannel or primary feed of WNEU, 2) purchase of either WMFP,WYDN or WWDP or 3) the unlikely scenario of going with NECN as the station. Not great options, but unlike Fox with WJZY, NBC already has a news presence in the Boston area, and will likely enter a "News Share" agreement with NECN for whichever option is chosen.
Plus, based on the wording of some of the contracts (particularly in sports with separate Cable/OTA partners), NBC may have to black out sports programming, the biggest portion of their viewership.
Based on all of these, NBC is just trying to get additional concessions from Ansin, with their only true option based on recent purchase history is moving NBC to WNEU, causing Telemundo to move to 60.2/WTMU-LP.