dealing with dropped event data
What you have described is that you want to consider the distribution of observations in a way that models the population to serve a better purpose.

I would recommend reading into how different types of distributions can be transformed so that your model might achieve a higher score.

In terms of your plots during analysis of your dataset, I would look at resampling at different frequencies, this will change how your plots will look and allow you to identify issues with seasonality, such as breaks in the account activity.

If the observations are missing because the person simply wasn't active, then this is a good representation of reality, the question is maybe how would you increase the users engagement?