For the record I don't want to split the party but I just couldn't come up with a true-to-character reaction to Alanya's histrionics and Seneia's doubling down on Rufio that doesn't involve him walking out in disgust.
Oh, and for the record, Rufio volunteered to enter the tunnel, and did so with several party members' consent/assistance, and no objections from the rest.
(see for yourself) Nope, he didn't rush in alone. ;-)
So we'll see how he does alone in the sewers. Good thing he's in his element. :-D