You don’t need to worry about losing data on the SSD after a reflash. It’s also listed here on the official guide, it’s the third bullet point under “Simple Solutions” Official Umbrel Troubleshooting Guide and FAQ
This is in reference to the initial setup it formats the SSD in ext4 if there is not already an installation detected, only when you’re first running through that setup process. Thanks for bringing this up I can have the team look into rewording this section… if there is already an installation and you already ran through the setup you can safely reflash the MicroSD with the latest version of Umbrel OS and it will take you straight to your dashboard. I just did it with mine too and logged right back in! 
In the case of any catastrophic hardware failures or anything else as long as you have your 24-word seed phrase as well you shoudn’t need worry about recovering as well, for peace of mind you can see the automatic recovery steps here too: https://twitter.com/umbrel/status/1562099972547690501