On import, if you use the copy function, LR will copy the image from the card to your disk and forget about the card and its content. If you never erase the card, you have a copy of the image until it decays on the card.
I import images from the card to my hard disk, into a folder in the chain LR Images, year, year-month-day. I do not erase the card until my backup software creates a copy of the image from its location in the hard disk. If the image in the hard disk becomes damaged, I can restore it from backup. LR will not notice or care that the image was restored, all of the change instructions are kept in the catalog, rather than the image.
Generally I have, at most, three versions of an image, the RAW, sometimes a TIF, and for printed images, a soft-proof virtual copy. Since I only print to one printer, only one soft-proof virtual copy is required.
This structure works well on a fairly recent Dell desktop running Windows managing the 28000 total images in my catalog.
Alan