Do they not display in 4k because Dell’s monitors are incapable? They make 4k HDMI cables. Its just that not all HDMI cables are 4k compatible, and not all graphics cards output at HDMI 2.1, which is 4k compatible.
Do yourself a favor and don’t use a splitter. One source, one monitor.

I’ll start with the obvious. Data restoration companies are your best bet. I’ve used them to great effectiveness, but they use a clean-room for a reason. Do not take apart your drive, or it really will be unrecoverable.

Does your computer recognize it at all, in any way? How long ago did you do this cut + paste? Days? Weeks?