At this point, Roe2 has to be the Summoner since she's guildless and already introduced. People have their bets on Kanami (or Demiqas) as the Monk, although at this rate, I doubt Kanami will make it back before the very end. But whoever the Druid will be is completely up in the air, unless Mamare decides that for one reason or another Serara will take up Nyanta's old offer again.
I feel like Serara will be their Druid. She might be in the Sister Guild currently but Serara already have both her feet in Log Horizon and only one hand in the Moon Alliance out of the sense of gratitude and duty for helping newbies. Once the newbies stopped being newbies which I believe they are, they'll just need one incident for her to make the switch.
I agree about Roe2 being their summoner too. On contrary I feel like their Monk class is the one up in the air. I feel like both Kanami and Demikas have a pretty low chance to be their monk.