It hasn't, and the B1G and the PAC won't want to try to break ours, as it would weaken themselves. Unless UVA and UNC have a change of heart, nothing is happening for 13 more years.
Should be at least 10-11 years of relative peace for the B12. Or at least chaos on our terms. When we have 2-3 years left, it might be more tempting for a conference to poach a team. Any more than that, and I can't see it... $30mil/year x 4 years = too expensive to leave.