If you hold all the Major Belts, then you can be considered undisputed. As to losing a belt along the way for any reason other than in the ring - it's a bit tricky. For example, Bowe dumped the WBC belt rather than face Lewis, which would meet the criteria of not having lost it in competition but, at the same time, not necessarily engender continued acceptance of him as the Undisputed Champion. In this case Lewis had a strong basis of dispute. Lewis, on the other hand, was poiliticked out of the WBA belt and it would be difficult to consider Holyfield's reclaiming of it, via the Ruiz I debacle, as a strong argument, given Lewis had effectively beaten Holyfield twice already. Technically and, therefore, 'officially', neither Bowe nor Lewis were undisputed once they were no longer in possession of all the Major Belts. But each were considered differently to varying degrees based on the circumstances of the dispossession. At no time could Wlad have been considered the Undisputed Champion. His brother vacating the title doesn't mean he can leave it to Wlad as an inheritance.
The WBA Have named Charr world champion. I can't remember which one but there's a vacant strap at heavyweight too. Not that I'd consider a vacant strap to be a dispute tbf.