Of course at the end of the series you would want to see her "ride into the sunset" happy. However, if she were to carry on through the series always happy, it wouldn't be very entertaining because it wouldn't make for much drama. If Sydney were happy, she wouldn't have any problems to overcome and there wouldn't be much drama. Would we be as involved if her missions had nothing to do with her family and her life? The fact that her life is intimately involved with what she is doing heightens the dramatic situation. And if, say, we pushed the angst onto other characters (say Jack) and Sydney was happy, it would be as though she didn't care . . . and that just wouldn't be Sydney.