Hi,
This is not a very simple case. Etcher, like any other USB burning application, essentially reformats the USB, and all existing files become inaccessible and some may be overwritten. To recover the USB in case of a failure, we point people to Etcher’s own documentation: https://github.com/balena-io/etcher/blob/master/docs/USER-DOCUMENTATION.md#recovering-broken-drives
However, you should not write anything to the USB until you have recovered as much as possible. This is not guaranteed, but a quick google search for “recover usb files” gives multiple hits. I cannot recommend any specific programs though.