Damage control scenario is what Wei Wuxian imagines, since this confirms what he'd been suspecting and what is a terrible plan all around: because the treasure, if the shard responds to or calls on it, is likely the rest of a mirror, and that's not something he wants the trading company to have, either. In fact let's lose the mirror shard down the seawell, can we? Keep everything broken but not in anyone's hands.

As far as handling the Concord's captain himself, Wei Wuxian would say be honest: they aren't sailors. They can't handle a ship on their own or take over this mission, and the sailors of the two pirate ships aren't going to trust them; they trust their captains. He'd advise that they continue with the original plan, and if Concord wants to be escort, keep itself friendly in the process, or wait outside of dead waters.