My mother had bypass operation, they took the vein out of her leg. Now she was in a bit of pain for about 1 week, but felt great and leg healed just fine. No you don’t grow another vein. I tell you though, mom could breath better and was so much better than before the operation. She was in hospital for 6 days, then home, very limit on walks, lifting for a while.
Here is a site to help you understand it more: