If you don't travel now, you might 'live to regret it'. [=you might feel sorry or disappointed about it in the future]
We 'regret' to inform you [=we are sorry to tell you] that we have offered the job to someone else.
It is to be 'regretted' [=it is regrettable/unfortunate] that the program has lost its funding.
(..) intentionally killing a man. Now she's gone, and we're about to do the very same thing. If you're asking whether you'll regret it someday... no. I don't think you will. To be honest, I crossed that line a long time ago... killing in the name of (..)2016 TvShow: The Blacklist Title: Alexander Kirk (No. 14): Conclusion Season: 3 Episode 23