Will I lose my Agent prompts when Agents are sunset?

Back up your prompts before sunset. Copy each Agent's prompt and run configuration into a local document so you have an offline reference. The migration flow itself also preserves the prompt inside each new Automation as you rebuild.

Your Agents are listed under Settings → Moby Tools → Agents (Moby 1) during the migration window, that's the best time to walk the list and save what you need. An offline copy means you're not depending on future UI state to recover a prompt.