I guess I am going to have to write some sort of "canned advice" with regard to failing hard drives which covers *all* the bases.
I simply presume that anyone using a computer knows of professional data recovery services and would avail themselves of same if their data were really precious and they can afford it. I have had too many clients with data that was precious to them, but for whom professional data recovery was out of the question financially, that I presume that anyone posting on a forum such as this one falls into that category. That presumption is not valid.
All of the above being said, it really depends on how the drive is failing that has the greatest impact on ability to recover data. If you have the tragedy of physical damage to the platters (I'm presuming a HDD here) then data recovery for that area is impossible. If you have a drive that's dying because its motor can no longer spin up the platters the probability of 100% recovery (and at great expense) is very good. I am generally willing to presume that the vast majority of drive failures are secondary to issues with partial corruption and have no connection to physical platter damage or drive motor failure. Or at least that's been my experience in the field with clients who had me recover data for them because they were not going to avail themselves of professional "clean-room level" recovery services. It was either partial recovery by me or nothing at all. So far, knock wood, those partial recoveries have been very successful and been very close to full, though sometimes with the need to slog through tons of data if I had to resort to something like the PictureRec (which recovers far more than pictures) utility that's part of TestDisk.
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall