In one of my first games in 1.23 as Moravia the HRE also got dismanteled, without my doing. This was because of all the Religious Center.
I was leader of the Protestant League in the midst of the league war against Austria (which provinces were 99% rerformed) suddly Austria died without an HRE heir, and noone else was found, so the HRE was dismantled. This war still continued, and I even won and took Religious Supiority, which didn't had any effect. Didn't continue the save for long, after I got my Achievment, since it was to weird.
I was leader of the Protestant League in the midst of the league war against Austria (which provinces were 99% rerformed) suddly Austria died without an HRE heir, and noone else was found, so the HRE was dismantled. This war still continued, and I even won and took Religious Supiority, which didn't had any effect. Didn't continue the save for long, after I got my Achievment, since it was to weird.