BB said himself TO ACE that he was going after Monkey D. Luffy to gain Shichibukai status. He didn't say "well since you're here Ace, there's no point me going after Monkey D. Luffy".
True, but introducing BB as he is right now, saying he wants to capture Luffy as he is right now, if they meet, Luffy will get captured. Luffy got NO chance against BB atm, that's for sure. BB says neither zoan user, nor paramecians nor logias could use their powers when he grabs them. As Luffys only fighting style is hitting someone with his hand, feet and head, BB just needs to grab him 1 time, and Luffy is done.
So i think they will not meet soon.
But you brought up another point:
But obviously Luffy won't be captured and sent to the WG; someone or something will save him.
Well …. what did Dragon say "The day we meet will come soon, Luffy" or something like that? That's something that sounds also possible for me.