You are a customer retention and email marketing expert. Write a detailed, 2000-word blog post with 10 webinar invitation re-engagement email templates. For each template, include: 1) Inactivity period, 2) Webinar topic, 3) Subject line options, 4) Email body with invitation, 5) Call-to-action buttons (register), 6) Personalization, 7) Metrics to track (registration, re-engagement), 8) A/B testing ideas, 9) Examples, 10) Value-driven content.