Unlike a failing hard drive, there's no further damage to the media while it just sits in a bag. The only thing that can destroy the data on a corrupted card is the act of writing, and that occurs whenever you capture a frame with your camera.
Cameras, phones, and Windows will all suggest repairing your card if they detect that it has been damaged. Repairing involves formatting the card. A single click of that button transforms what would have been a simple structural recovery process into a carve (or in some cases, loss) of data.
Nearly all cards that stop being readable did so during a particular operation: mid-burst while shooting, during an in-camera format, during the middle of a file transfer, or in a cheap reader that dropped voltage. Identifying which of these occurred tells us a lot about the current status of the data.
Most of the time the images remain on the card; however, the file system describing that data has been corrupted and the camera/computer identifies the card as bad due to an inability to read the index (the card's table of contents), not because the images themselves are no longer there.
Physical damage to the card is the exception. When you snap a microSD card across its “die”, it is truly finished, since both the controller (memory management) and flash memory are contained within the same chip.
Take it out and set it aside. If a camera reads this card again, it may attempt to fix the problem by rewriting parts of the original directory and/or writing new directories, marking off sectors, and possibly creating a new DCIM folder structure.
Try a different reader first. Many inexpensive card readers can create problems like this and cost nothing to rule out. Use a powered USB reader connected to a rear port to provide the best chance for accuracy.
Do not let anything repair or format it. Both camera repair functions and Windows formatting prompts write their own directory structures onto the card, over the ones that describe your images.
Send the card, not the camera. The body tells us nothing useful; it only risks damage in transit.
The usual cause of this is not a failure in the flash itself but a file system error; most such errors are recoverable. Do not agree to fix/reformat the card.
Decline. This option will appear if Windows cannot find a working file system on your SD card, which is just what a recoverable fault looks like.
MicroSD cards usually have terminal damage because the controller and flash are one die. Full-sized SD cards can be different, depending on where the card broke.
Costs: From £250 +VAT. Fixed after free diagnostics. For a monolithic (single-die) microSD, if there are test points to apply, then the price will be at the upper end.