They last forever however they can die. When they die you have to get the "grass of life" from the stables for 50k to res it each time. The horse/camel health kits work for the wolf. So, you can heal him with those kits. The abnormal potions also work on the wolf. You can get all these items at the stables. The white wolf and the gray wolf are exactly alike, so in my personal opinion save your real money/silk for something else and get a gray wolf. They are 1m at the stables. The only difference is the color.
They start out at lvl 1. I leveled mine to lvl 26 at the Hyungno ghost. They are non-aggro so my wolf never died. Also while they are still small and you are hunting higher lvl mobs, turn his attack off. This will also save you money for ressing him. Now when you are grinding on mobs that are the same lvl or below the level of your wolf, you can let him attack. He'll help to kill the mob quicker.
The best of luck! And Happy Grinding!...
The monkey is the same way, can be swapped between chars but not sold or traded. Hope this helps guys!!