Bella goes back into the bar to ask someone relatively unoccupied for more information about how this place works. She comes back armed with the results, shares with the group, and budgets a few more hours to stay and talk to Etty before it'll be ruinous to her sleep schedule - the holiday will be over soon and Celo will thereafter be in violation of Milliways rules, anyway. Any of them may find a door again in the future, so it's not necessarily goodbye forever; even if they aren't there at the same time they'll be able to leave notes at the bar.