Unlike a failing hard drive, nothing is getting worse while it sits in a bag. The only thing that destroys what is on a corrupted card is writing — and the camera writes every time you take a frame.
Cameras, phones and Windows all respond to a corrupt card by offering to repair it, and repair means format. That one tap turns a straightforward structural recovery into a carve, and sometimes into nothing.
A card that has become unreadable nearly always did so during a specific operation — mid-burst while the camera was writing, during an in-camera format, halfway through a copy, or in a cheap reader that dropped voltage. Which one it was tells us a great deal about the state of the data.
In most of those cases the images are still physically present. The file system describing them has been damaged, and the camera or computer reports the card as corrupt because it cannot read the index rather than because the content has gone.
The exception is physical damage. A microSD card snapped across its die is genuinely finished, because on those the controller and the flash are one component.
Take it out and set it aside. Every time a camera mounts a damaged card it may write to it — rebuilding a directory, marking sectors, writing a new DCIM structure.
Try a different reader first. Cheap readers cause exactly these symptoms and cost nothing to eliminate. A powered USB reader on a rear port is the fairest test.
Do not let anything repair or format it. Camera repair functions and Windows format prompts both write new structures over the ones describing your images.
Send the card, not the camera. The body tells us nothing useful and only risks damage in transit.
Usually a file system fault rather than flash failure, and usually recoverable. Do not accept the offer to repair or reformat.
Decline. That prompt appears whenever Windows cannot read a file system, which is exactly what a recoverable fault looks like.
On microSD that is usually terminal because controller and flash are one die. On full-size SD it depends where it broke.
From £250 +VAT, fixed after the free diagnostic. Monolithic microSD requiring test-point work sits at the higher end.