Kepli would miss her pal Sid. But I understand when a character doesn't come together the way you would like and you need to change it to something different.
I found the solution to why I don't like Siddhartha. It is extremely frustrating to me to roleplay dumb characters (low INT scores). I can deal with the other attributes in the dumps, but not that one. Siddhartha is the first one I've played with low intelligence.
There are two issues, here. The first is character rebuild, and the second is character replacement. As already mentioned, a character gets one 'free rebuild' during their career. This doesn't change who the character is, it is merely a shuffling around of the character's abilities to be more to your liking.
Then there is character replacement, which can be voluntary or, for practical matters, compulsory (such as a death with a resurrection cost higher than the character can afford). Then you're introducing an entirely new character to play in lieu of the first. The rules for that are different, and it's easier just to cite the link than explain them: http://livingpf.wikia.com/wiki/Category:Retired_&_Deceased_Characters
Short form:
(1) "I think Sid would work if..." -- character rebuild (once/character)
(2) "I hate Sid and he won't be enjoyable regardless of what I do..." -- character replacement (see rules)