Is a divorce considered an irreversible or a revocable one, and is the waiting period (iddah) obligatory after divorce, in the case of doubt regarding the consummation of marriage through valid seclusion?

The waiting period ('iddah (definition)) is obligatory for your divorced wife, according to the majority of scholars, simply by virtue of a valid seclusion (khalwah sahihah). The Shafi'is differed, not obligating the 'iddah unless there was actual intercourse, but they do obligate it in this case if ejaculation occurred into the vagina. As for the Hanbalis, they apply to a mere valid seclusion all the rulings that apply to consummation, including the permissibility of taking back the divorced wife (raj'ah).