If anybody interviewed and didn't get the offer but is debating about going back after six months, I would say do it! I interviewed last summer, went back recently and was fortunate enough to get the offer. I know rejection is always hard, but I was really impressed how grateful they were that I came back.
A few members of the interview team even remembered me on a personal level, which says a lot about the type of people that work at F9. If you want the job stay persistent, it goes a long way at the interview.
There is a lot of excitement at F9's headquarters, it's infectious. They really believe in the ULCC model, the company, and improving the next contract.
It's my belief that F9 has a solid future, and the ULCC model has some real staying power. I consider myself extremely fortunate to get on at such a exciting time. Good luck to everybody!