Gorum speaks then, after the fashion of gods.
He shows them the evidence of Zon-Kuthon, in fact, specifically instructing His people, directly after Otolmens's order, to violate Her edict in Pharasma's Name.
Gorum has been persuaded.
He is obviously not willing to go along with Zon-Kuthon's destruction; that would give the portfolio of Lawful Evil to Asmodeus nearly alone, with reverberant effects at the deepest levels of reality. But let Zon-Kuthon be sealed up away as much as Zon-Kuthon can be sealed, in a vault to which Iomedae alone shall hold the key - not that Gorum would object to holding that key Himself, of course, but this seems like a job for a Lawful deity opposed to Asmodeus - to be released only as a counterweight to Asmodeus, if that becomes necessary. Asmodeus will be strengthened by this too, of course, and not trivially, but that is a price Gorum would sooner pay than see Zon-Kuthon release Rovagug.