If you assume that a tulpa has independent moral value from their host from the moment they are conceptualized, then allowing them to fade at any stage is unethical, as well as what happens to most imaginary characters in general. If it begins after they are independent, then the early stages of tulpamancy can be backed out of "blame free" and most cases of dissipation and merging later on are also blameless due to the consensual behavior of the tulpa. If individual systemmates are only of moral value in so far as they make up a part of a single living body, then most of this is moot and the only thing that matters is what arrangement of tulpas and/or host is most beneficial to the system.