What's the (mental) quality different between aversive leaving (vi-bhava) and renouncing (nekkhamma)?
Vibhava tanha arises as a result of attachement, aversion and ignorance combined with the wrong view of Nicca, Suka , Atta and Subha. 
Nekkhamma is a result of non-attachement, non-aversion and wisdom combind with the right view of Anicca, Dukkha ,Anatta and Asubha.