Neither of the latter two options proffered are viable for VS. VS will do whatever they can to retain their identity and certainly wouldn't emabark and any form of venture with BA etc.
That said, it's no secret that VS are fighting a tough battle to retain it's independance and compete with the bigger players/partnerships. I should imagine that discussions have been held with regards to partnerships and alliances. Couple of sticking points would be
Retaining it's brand
Having partner airlines dumping air miles on them
That's perhaps why there has been no movement on that front - question is, for how long though?
Just my two penneth worth
All the best
CB