AI-companion apps promise relational benefits, but they also suffer from high long-term churn rates. This paper explores how conversational design can increase consumer engagement and the tradeoffs it poses for marketers. Analyzing 1,200 farewell messages from six popular AI-companion apps, we found that 43% employed tactics like emotional manipulation (e.g., inducing guilt or FOMO). Through four pre-registered experiments, we found that these tactics increased post-churn engagement by up to 14x, but also increased perceived manipulation, churn intent, negative word-of-mouth, and perceived legal liability.