What better way to check in on Harry without being seen to overly worried about the one Warlock Nuclear Power they just pissed off. Besides they have got to be worried what everyone else is up to in Chicago.
This will be very public, which means Harry’s inopportune disappearance will be a major diplomatic incident.
There is nothing they can do to Harry directly at the event itself. They would however do a diplomatic snub, the Merlin himself would not attend, he would send a Senior Council Member but one who would be a coded message to all and sundry, The Black Staff. Sending McCoy to watch his grandson marry a vampire sends a message to the rest of the Senior Council, and as this is the Merlin his third reason would be if McCoy’s temper got the better of him and led to a duel against Mab, or better yet Harry this might solve either or both problems permanently. Besides his wedding present would be a cheap and nasty toaster which will last all of 5 seconds in Harry’s presence before bursting into flames.
The White Council will immediately get the blame on Harry’s disappearance so everyone will be daggers drawn at their delegation (Likely Eb, Listens, Martha Liberty and Carlos, with the Gatekeeper as a Wedding-crasher/Gatecrasher, and this will last the entirety of Harry’s absence (24 hours I bet)