[Zeke]

Doesn't matter. Once you begin the offer/counter offer process with anyone, they represent you on that property. If the listing expires and you buy the property from the seller direct, both the former listing and buyer's realtors can and will sue for the commission.
The only way around John is his broker. If he is the broker, the real estate board. Or, as many have already suggested, clear the slate and start over with all new players.