As part of my job, I interview several candidates for various positions every week. I've already handed in my notice and I'm currently working my notice period.
One big factor for people when deciding to join (or not to join) a company is the people, and that especially includes the interviewers. It has happened to me that someone I interviewed joined the company and I left shortly after that, leading that person to quit as well, given that I was one of the reasons for him/her to join the company. This is more expensive than the candidate deciding not to accept the offer at all. At the same time, I believe teams should be as transparent and honest as possible, without harming their business, of course.
Should I let the interviewee know that I'm leaving the company? This would be done in a subtle and respectful way, without badmouthing the firm, and probably not during the first interview. The pros and cons of telling them and not telling them are pretty clear, I believe.