Apps · Drive, safety and recovery
What happens to my moved or offloaded apps if my external drive fails?
Short answer: Apps stored only on a failed drive are lost; reinstall them. Moved apps keep their settings on your Mac, but offloaded apps' data was on the drive — so back the drive up.
Apps stored only on that drive are lost with it, so reinstall them from their developer or the App Store. For moved apps that's usually painless, because their settings and data stayed on your Mac. Offloaded apps kept their data on the drive too, so that data is lost unless the drive was backed up.
Storage Studio is about freeing space safely, not replacing backups — keep a Time Machine or other backup that includes your external drive.