The thing with Bill saying goodbye to Lee. I think Lee knew what Bill was going to do when Laura's time was near. Perhaps they had discussed it, or maybe Lee just knew his father.
Bill decided to fly until Laura died. When that happened, he would land wherever they were and build their cabin there. He didn't know how far he'd get, but knew it would be far enough that, after disassembling the raptor for parts, it was highly unlikely he'd ever see anyone again.
Or at least, that's what I got out of those scenes.