I want to begin by saying that I don't have any direct experience with the firing of tenured faculty, nor am I intimately familiar with Title IX issues. In particular, the requirement mentioned by the OP regarding Title IX training for all faculty are not in place at my (public, US, research) university.
But I do have experience with the way universities and university administrators work. For instance, I had a colleague who in his first year did not want to sign a standard intellectual property agreement (which I have no memory of signing upon my arrival two years before, but I assume that I must have done it). It seems like a somewhat analogous question to ask: would the university fire this (untenured) person? The answer that I would give to that is "Eventually perhaps, but there would be a lot of intermediate steps, and the professor would have to be durably intransigent in a way that tired out the higher administration and their lawyers." In the particular case at hand, this issue went on for several months, and my colleague was satisfied by being permitted to sign an earlier version of the intellectual property agreement that he found more favorable.
As another example, every once in a while I am required to take an online test to make sure I am sufficiently cognizant of certain current laws: not related to Title IX but rather to FERPA. How does this work? In many stages: there is some announced deadline, and as it approaches I get reminders from someone in my department. If I miss the deadline I will get more personalized, urgent reminders. If I were durably unresponsive then (I am told) I will get locked out of access to certain student records: e.g. I would not be able to look up any student grades online. The idea here is that if my lack of training is viewed as a liability, the university will take steps to remove me from the specific situation that is causing the liability rather than suspending me generally. Of course, being removed from that situation may cause annoyance or hardship for me, and it may even interfere with my job.
Coming back to the question asked: in my own opinion it is very unlikely that a tenured faculty member would be suspended or fired for not complying with a Title IX training course...at least not as a first or even fourth step. Rather the university would on the one hand take steps to assess the liability involved in that specific faculty member not having the training, and if that liability feels considerable to them then they will try to reduce that liability while keeping the faculty member and/or squeeze the faculty member in such a way as to make carrying out the training preferable. By the way, there are many ways that an administration which is unhappy with a tenured faculty member can make that faculty member's life less pleasant which completely circumvent the expectations surrounding tenure: e.g. they could mess with the teaching obligations of that faculty member, regulate or limit their access to certain groups of students, give them less of an annual raise or no raise at all, and so forth. If the administration really thinks it is dead right and you are dead wrong, I think that they can, while keeping you around, make life more miserable for you than you can for them. In the case of the OP, he says that he will just leave. Exactly: that's a much more likely outcome.
I think that in order to consider suspension or firing in the short term, the administration would have to find some specific, actual legal liability rather than just a potential one. If a university fires a tenured faculty member for their own interpretation of a federal law, the probability of a huge fuss including censure from faculty associations and unions and/or a big lawsuit seems rather high. I would expect them only to risk that in the face of some other similarly proximate scandal or lawsuit. Another answer contains a link to a university band leader (untenured) who was fired for refusing Title IX training until after he mishandled a sexual harrassment / assault case between students under his direction. In that case they pretty much expect legal action either way, and they're weighing one lawsuit against another. If the OP has not had any actual dustups or issues with students, I would be absolutely flabbergasted (note: this could happen, obviously!) if he were fired rather than squeezed or forced out in a more subtle way.