Well... If Woundwort didn't meet Vervain in third season, then the latter would have been killed by an elil, but I agree that Aspen purpose was to show Vervain's good side. On the other hand, Aspen didn't have to die to serve that purpose and besides it wasn't the only time Vervain shows the potential for changing. When the Redstone is about to be destroyed he suggests giving a warning to warren's rabbits, for example.