There have been a few which went back to NBC,
most recently (I think) WDTN/2 Dayton, OH in 2004.
Most of the ones that went to ABC and back to
NBC were in medium and smaller markets:
WTLV Jacksonville, FL
WSAV Savannah, GA
WJHG Panama City, FL
KCEN Temple-Waco, TX
KOMU Columbia-Jefferson City, MO
I believe WBRZ channel 2 in Baton Rouge abandoned NBC for ABC back then. It has not reverted. I recall one of the WBRZ honchos at the time saying they were fed up with poor-performing NBC programs. Interestingly, the parent station, WJBO 1150 AM, was BR's original NBC radio affiliate.
KTVE Monroe, LA/El Dorado, AR
The bigger ones, like WSB, KSTP, WRTV, WSOC, and
KGTV seem perfectly happy with ABC, although I think
KSTP and WRTV did take a ratings hit at the expense
of (respectively) KARE and WTHR, I think the prevailing
wisdom was well expressed by WSB g.m. Fred Barber when
he made the switch in 1980: "We're not thinking about the
November ratings book (he made the switch on Labor Day,
September 1); we're thinking about where we're going to
be in 10 years."