More details: Reviving characters sometimes fail. Reasons could be: 1) The character doesn't wish to return to life. 2) Precautions were taken to avoid resurrections. (Expect that people executed always fall under this category) 3) Magic capable of destroying immortals were used in the slaying. Characters killed due to bad luck in adventures or on the field of battle where your opponents doesn't have time to claim the body should be easier to resurrect, as the only stopper would be that the character doesn't wish to return.
Q: Do I control if my character wish to return to life. A: No.
Q: Is there ways to negate the listed ways that could prevent resurrection? A: There are a few ways but nothing easy. It could be adventures with not many other benefits than allowing a resurrection on a success. Expect anything less than extraordinary success to require the sacrifice of one or more adventuring members upon the resurrection ritual. Expect challenge rating of the adventure to be at least CR 10 and most likely higher.
On a lore note, the answer to the last question is the reason why Camelot has such distaste for magic-users--King Uther more or less refused to accept the principle of magic being used to trade one life for another, and rebelled against it with the Great Purge. So it has a uniquely sensitive history, too.