UPDATE: According to the RNC's official statement, the debate will proceed, but will be carried by CNN instead of NBC.
According to Politico, the RNC has voted to officially sever ties with NBC for debate coverage, which will have the result of canceling the scheduled February 28th debate in Houston. The move came after the debacle of a debate hosted by CNBC back on October 30th that was widely panned (by critics on both the right and left) as one of the worst jobs any network has ever done of hosting a debate.
Since then, The RNC has been in negotiations with NBC to hopefully avoid a repeat experience, but those negotiations have broken down.
Hard to say that this is the wrong move for the RNC. There isn't a trustworthy NBC property on television right now, and none of the candidates will be well served by fielding dumb, gotcha questions from openly biased moderators. By February 28th, the field will be winnowed down to the serious candidates, and there's no use exposing one of them to NBC's liberal stupidity.
Meanwhile, the GOP debates have been a ratings bonanza for every network that has carried them, due largely to the presence of Trump. The CNBC debate was by far the highest ratings that network ever received, and given NBC's struggles (particularly in the increasingly vital live television arena), they stand to lose a pretty significant advertising windfall over the decision.