Dyck must be kidnapped at once and carried out of Ireland.
It would be simple.

A little more drugged wine, and he would be asleep and powerless--it had already tugged at him.

With the help of his confreres in the tavern, Dyck could be carried out, put on a lugger, and sent away to France.
There was nothing else to do.

Boyne had said truly that the French fleet meant to come soon.

Dyck must not be able to give the thing away before it happened.