It is absolutely impossible to end conversations with most of my friends. Every time either one of us starts to say goodbye, we either have one more quick story to share, or we make one parting joke.
The problem is that it invariably leads to one more story or a follow-up joke. Suddenly, we've gone from winding down to being at full speed again. This is why going to dinner with the right people lasts 4 hours (or until we are politely kicked out because the restaurant is closing).
When conversing with good friends, it's wonderful. When writing dialogue, it's lousy. And when trying to find that final sentence to your writing, it's murder.
Keep it short and sweet. Everything within reason, but shorter is sweeter.