In player vs. player designated zones, you will still be viewable and attackable by players, but you are not left completely defenseless. While engaged in a Pet Battle, any attack from another player will break you out of the battle. You will receive a 3 second damage shield that will absorb 50% of incoming attacks. The same exact wild pet that you were previously battling will respawn after you come out of combat with the other player. However, if you defeated the primary pet in battle prior to leaving the match, the pet and its team will not respawn.
A zygor guide is absolutely not a reliable investment, it's not going to be resaleable so you're never going to make your money back. As a purchase, at this point in the game if you need a leveling guide you shouldn't be playing the game. Leveling up is so fast, quests are easy to understand and chained, and the game puts a mark on your map for where to go for around 90% of quests. If you can't manage to follow in-game quests (possibly with a free add-on), what do you plan to do when you're done leveling? Raiding and PVPing don't just happen for you automatically.