The lack of football didn’t prevent Villanova from winning 2 of the past 6 national championships. It didn’t prevent Gonzaga from getting to 2 of the past 5 title games. It didn’t stop Loyola (Chi) from getting to the Final Four 4 years ago. There’s no way that the lack of a football program will kill a good basketball program.
Attendance didn’t drop just because some of the teams were below par, seasons, by the way, for which there were expectations going in but injuries helped to ruin. A big factor in the massive decline in attendance was the fact that the games were against opponents no one cared about and half the fans didn’t recognize.
Regardless of how good basketball is in the Big XII - and I agree that it has been very good in recent years - the same problems would exist as was the case in the AAC. There would be no meaningful rivalries and no tradition. The opponents wouldn’t be bringing any fans with them because of the distance - as opposed to Big East games when attendance is/was bolstered by fans of the opponents buying tuckers. The trips are too long and wear down the team to a greater degree than opponents in a conference which is centered much closer to most of those other members.
It would be a different story in the ACC where membership would make much more sense. Everyone would be in the same time zone. Trips would generally shorter. And you actually find alums of many of those colleges here in CT or within driving distance. The ACC includes some traditional rivals, names that are recognizable to just about everyone in CT, and schools which might even be attended by other members of the same family.