We don't store your sensitive health data on servers (so it is not in the Cloud). All your data stays on your device unless you choose to share it with someone in your Circle of Trust.
So, if you didn’t share your data with anyone and didn't back it up on a desktop, then yes... It's lost, the same way it would be if you had written it all down in a notebook without making copies.
The fact that we don’t keep a backup of your information reinforces the security and anonymity we give your private health data.
Want to do a backup of your data? You have several ways of doing it.