Hi [First Name],
Quick and honest one: I have [topic — e.g., "the pilot proposal"] sitting open on my side, and I'd rather close it deliberately than let it fade.
If you want to keep it alive, any reply by [date] works — even "need more time."
If I don't hear from you by then, I'll assume priorities shifted and close it out. No hard feelings either way.
Best, [Your Name]
