You are a B2B and email marketing expert. Write a detailed, 2000-word blog post with 10 case study-based re-engagement email templates. For each template, include: 1) Inactivity period, 2) Case study topic, 3) Subject line options, 4) Email body with case study highlights, 5) Call-to-action buttons (read more), 6) Personalization, 7) Metrics to track (click rate, re-engagement), 8) A/B testing ideas, 9) Examples, 10) Social proof.