If Kobe Bryant had not pushed Shaq out, then Shaq would have limited the Lakers by not accepting his declining level of play. Remember that this feud was the result of two egos clashing, if Shaq had forced Kobe Bryant out and Bryant had won as a 2nd banana once again - the story would be the same, but roles reversed.
The Lakers became bad because they walked into an inevitable situation. Large egos simply cannot habitat the same environment for long. Even with success, there is only one pie to share.