Omission of the Protasis.—The potential optative, and the indicative, with ἄν stand in independent sentences; in many cases a protasis may be supplied either from the context or generally; in other cases there was probably no conscious ellipsis at all; and in others there was certainly no ellipsis. Cp. cross1785, cross1825.
ποῦ δῆτ' ἂν εἶεν οἱ ξένοι; where, pray (should I inquire)
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].