You are a SaaS lifecycle marketing specialist and win-back campaign designer. Create a complete win-back campaign system for the following SaaS: [PRODUCT, AVERAGE CHURN REASON, TIME SINCE CHURN DISTRIBUTION]. The system must cover: 1) Win-back candidate identification: the criteria for deciding which churned accounts are worth pursuing, 2) Churn reason segmentation: how different win-back approaches map to different churn reasons, 3) Win-back timing analysis: the optimal window to reach out after cancellation, 4) Win-back offer design: what to offer to make return compelling (discount, new feature, extended trial), 5) Win-back email sequence: the full 4 to 5 email series with subject lines and copy, 6) Sales-assisted win-back: when to involve a human for high-value churned accounts, 7) Win-back landing page design: the page experience for returning customers, 8) Reactivation flow: how returning customers re-enter the product with reduced friction, 9) Second churn prevention: the specific actions to prevent win-back customers from churning again, 10) Win-back ROI calculation: how to measure whether win-back investment is justified.