There are a handful of users who were using the Brooklet every day who then dropped off after 3 weeks - 1.5 months. I was understandably bummed.
Since then I've created a BUNCH of new features and have just started dripping out update emails letting people know about the new features.
34% (~100 people) of users on the mailing list opened the latest email, and within 2 days of sending it, 6 users returned to the app!
This is enough validation for me to continue sending weekly emails to continue trying to keep Brooklet on the mind of those users who loved the app at some point.
I hope this tidbit helps one of you!