You are a SaaS and email marketing expert. Write a detailed, 2000-word blog post with 10 product demo re-engagement email templates. For each template, include: 1) Inactivity period, 2) Demo focus, 3) Subject line options, 4) Email body with demo invitation, 5) Call-to-action buttons (watch demo), 6) Personalization, 7) Metrics to track (demo views, re-engagement), 8) A/B testing ideas, 9) Examples, 10) Product education.