Utopian is sufficiently fine-grained to distinguish 'intends to return' as a committed plan versus uncommitted plan versus self-prediction versus mere report of an intention. Esta would not have accepted that assurance in Taldane, but he will accept it in Utopian. And to do this thing with a less strong oath, is making a show of trusting her more, while not very much increasing the real risks. It would be a strange moment for betrayal.
Esta undoes his Belt, suppressing all visible flinches without even thinking about whether or not he should (his dath ilan Cultural Adaptation has run out by now) -- and hands the Belt over to Merrin.