4-->下下策：太急。And you assume too much risk in today's market condition.
3-->下策:太緩. No one can guarantee anything. No guarantee can be followed through (in your group's specific situation). I don't think you will gain anything by asking for a unquaranteed quarantee, instead you pay the price that now they know you are not happy. Your boss might not be that bad, just she is not so courageous enough that she chose lying to avoid problems (having the courage to be honest sometimes is the best choice).
1-->上策. Still太急. Seems price tag to you is too steep without a pay raise.
2-->上策. But you need to be very creative in justifying it and help your bosses to justify it to their superior. Many times, it is not that the bosses refuse to give you a raise. Their hands are tied. You need to give them ammunitions to fight for you.
I would suggest below in the order of execution:
(1) *Unofficially* go for the VP. Informally convince the decision-makers that you are the ONE (this is the key). *Then*, make it very clear upfront that you demand a raise for the transition. They will have to fight for the funding. If they come back with "yes", congratulations! O/W, back out and procceed to (2).
(2) Talk to your boss (she is powerless; just keep her in loop), her boss and probably her boss's boss: you are willing to pick up extra resposibility left behind by B (nobody can ask for an internal raise without assuming more resposiblities right now). AND you want a raise together with that. The raise could come in different forms. For example, retention bonus.
(3) In the meantime, keep close contact with B. B is testing the waters out there (for you :)). Wait for half a year or so, as well as seeing what comes out of (1) and (2).
Good luck.
