Obviously none of them want to skip debates. The bet they would be making is that if thy threaten the RNC with skipping the RNC will find a way to kick Trump out. I bet you anything that some of the campaigns are sniffing each other out on this issue, but would only do it if they got to some kind of critical mass where a bunch of them all agreed and issued a joint statement.
True, but as you said, Trump has a big of an ego. An insult like that would likely inspire him to go third party. And even if they wanted to, he is leading the polls or a least in second place. I just don't think they have the capital to pull it off.
I also found this old article when Trump was polling at only 6 percent, which suggests it's not possible to disinvite someone who meets the qualifications without violating campaign finance laws.
http://www.nationaljournal.com/2016-elections/why-republicans-can-t-kick-donald-trump-out-of-their-debates-20150708So I think the networks would be forced to call the candidates bluff.