I think it's a pretty good sign of a healthy church when people want to fellowship, even loudly, after the quiet intensity of worship, so I think it's best to just go with the flow. In fact, I've pretty much done away with the big bold postludes and instead I play another stanza or two of the closing hymn, perhaps making a little improv on it, or perhaps modulating into another one of the day's hymns, but keep it pretty low-key. No use trying to compete with or out-shout the enthusiastic talkers. When I used to play in a larger church, I could get away with playing louder postludes because the organ sound wasn't so concentrated, but in the current 200-seat sanctuary, organ music at ff pretty much dominates the space.
I'd rather people leave the service grateful for the music they heard rather than racing for the door to get away from it!