How to avoid/prevent offloading of emergency response app

I’m with a major Canadian university, developing an app to help users plan for and respond to local hazards, like earthquakes and flooding. Since this is the kind of app you set and forget until an emergency occurs, and there’s a good chance internet access won’t be available to re-download the app once a disaster occurs, what can we do to help our users avoid or prevent offloading of the app?

Encouraging users to disable offloading seems like overkill. What other options would you suggest to help avoid offloading in the first place?

Thanks!