If you are interested in continuing to play, you do not need anyone to replace you.
If you don't trust what your alliance leader does, you won't leave your replacement.
If you feel part of an alliance and do not want to leave it, you should not be forced to give your replacement to another.
In short, if you have rights and obligations for your alliance, you, personally, must decide if you want replacement and who should control it.
Also, that there is a limit of use of substitution already implicit in the game itself, it is not infinite in time.