No. 'Synthetic leather' is generally a vinyl or PU product. However there are some products such as bonded leather or eleather that are made up from scraps of leather that are bonded together - these...
Cows themselves have to be killed in order to give up their skins to be made into leather. It's the HUMANS who make the leather, and make it into shoes, belts, chaps, jackets, basketballs, baseballs,...
Many different things could happen, good and bad. People will have to find some other source of protein and Vitamin B12; ranches will no longer become cattle ranches, but perhaps sheep, bison or elk...