I struggle seeing Hagar return due to Wolfgang, management, it being personal, plus losing his voice badly the past year (he is 67 so not knocking him for that).
Roth and Van Halen are a huge pain in each others ass and a clash of epic egos but never really was that personal.
The simple truth is likely we will see. Clearly Roth did had issues (medical/personal whatever) on ADKOT tour and in 2014. He should up in 2015 not having his shit together and Eddie was clearly frustrated. Dave however did get his shit together and delivered a better than expected tour. So now Wolfgang has his thing, Dave is in LA which is a good sign, and Eddie seems content watching as proud dad what Wolfgang does. So Van Halen is likely a big we will see which is probably the most frustrating answer for fans. Optimistically Wolf does his thing, Eddie releases his book next summer, and then they see if Roth will play by their rules and record a new record in 2017. Worse case Wolf does his thing and Eddie just piddles around eventually doing dome instrumental music. I don't think Eddie ever records with another vocalist or tours with Hagar. I'm sure they will fan the Van Hagar flames and Dave is out, we hate each other story line since it simply works for them getting fans riled up more so than we do not know and I;m watching my kid do his thing so frankly don't really care now.