Hawkeye did not lose his leg in the comics. This kind of major physical change didn't occur for him. The comic writers chose to keep his physical condition consistent without introducing such a significant alteration.
Well, from what I remember, it might have been a result of a powerful enemy's attack. Or perhaps it was a risky move she made to save someone and ended up losing her leg in the process.
Odin's loss of his eye was a significant act. He did it to gain profound wisdom and insights. This sacrifice was part of his journey to become a more powerful and knowing deity.
The bear lost his tail because he was tricked by a fox. The fox told the bear to put his tail in the hole in the ice to catch fish, but when the ice froze, the bear's tail got stuck and broke off.
The bear lost his tail because of his own naivety. A fox tricked him into staying in a frozen hole for too long, causing his tail to freeze and break off.