First define "successful" and make sure others would see it as the same. If growth is stagnating, that's not what success looks like in an app.

The only way you have a chance at selling it at anything above "fire sale prices" is you can say that you have enough actively engaged users, which is primarily DAU/MAU, then you have a chance of selling the users to someone who wants those users but it's still really tricky.

Happy to talk through it in more detail with you.