There are no rules for it, because you don't need rules for it.Where do you find in the rulebooks about the part where you can make up to a number of PCs as backup character since dying in dark sun is more often than any other setting?
There are no rules for it, because you don't need rules for it.
It's just a precaution that you, your fellow players and your DM might want to take.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.