Nebula contacted Mantis after escaping Thanos and told her that they should go to Titan
I must have missed it, I recall Nebula limping along after she tricks the guard to come closer with her eye by keeping it from connecting to her body, but I don't recall the conversation between Nebula and Mantis... why Mantis? did they have some connection or reason she wouldn't have tried to contact her Sister or Starlord.
I'm not saying you're wrong, I've just seen it once and poured what I remembered into the OP a few days later.
Why not check me out on youtube and help me on the way to 2k subs over at www.youtube.com/stormcloudlive