If that happens, don't even allow that thought to linger my friend! The changing of the topic, for all we know it really just popped into their head and they said it out loud and just after realized it was rude to change the topic. Honestly this happens to me all the time ironically, lol, you can see it in my video's, I say one thing, about to continue and then change the wording entirely because I thought of a different way to say it, or something else entirely I wanted to say first and then come back to it. Either way as I always say, it's all about the state of mind. People say they just outgrow it or what ever but it likely depends on how they feel about it, maybe having to do with what their job is like, how used to the job and life they've settled into has gotten, does their day to day rely on any pressured speaking like meetings or what have you and how used to it they've gotten. The odd thing is that even though we don't know how it's happening and why we trip up, we know that how much we worry about the situation effects it, the stress, the pressure, we feel it simply because we don't stutter alone talking out loud or in the shower, etc. So don't even think about whether people will leave or change the subject and if they do just don't let it get to you and focus on what they're saying or what you wanna say next, not HOW you wanna say it because it might bring up that tightness and it's like a viscous cycle if you stress over it, think about it, starting a never ending stress bout. Just let it be and think about anything else, I got so used to it I break out of any pressure I feel by saying in my head "bah" and move on. I might feel kind of winded and tired after it but I'd continue to focus on the subject matter, where I am, anything else and slowly I get back to fluency in the sense that I don't need to stay quiet anymore. It's tempting to stay quiet after a run of stuttering. You don't need to pressure yourself to talk of course but can take all the time you need to relax and feel the tightness and blocking let go of your throat, easy breathing, continue not thinking about it, and come back to the fluency state and better mindset.