No contract no fee, no agency, no fee due. Also at the time that agent was representing the seller, cant be a dual agent without full disclosure and approval of the parties. But seller has no obligation to compensate that agent as the home is not on the market and no fee being offered. And the agent now represents the buyer.
I believe you were considering the agent as a procurring cause. Not so, as it is not on the market.
All would be open to negotiation. But your also makiing many assumptions, listing agent, showing buyer other homes, buyer is not represented presently by buyers agent, Sellers former agent, becomes agent for the buyer and so on.......
The question was is the seller obligated, simple answer, contract stipulates grace period, or if seller wants way around grace period, go to the 500 entry only brokerage companies. Isn't real estate getting to be fun
When I use to represent buyers for commercial deals, buyers paid my fee. That is buyers brokerage - reason that is not done in residential is due to they have not found a way to include that fee in the mortgage.