Two headed snakes do happen from time to time but generally they are dead straight out of the egg. Ones that do hatch out usually die right away, some that do survive usually don't last for more then a couple years. So really lucky ones can last a few years but that is really rare.

If you ate wanting one as a pet that probably ain't gonna happen the survival rate is too slim an because it is something special a snake that would normally go for $100, if it had 2 heads and looks like it has a better chance of survival,they can go for thousands. Most that do survived are also used for studies not pets.