I'm not really sure that this is a good idea, as in my opinion it will set a bad precedent to be hosting a novel after the translator removed it at the authors wishes.
Furthermore, it also sets a bad precedent to be hosting novels in general, because if you mirror this novel, why not start mirroring other novels? Eventually you move on to mirroring ongoing series which is a huge malus as far as the novel scene is concerned, as it ends up drawing 90% of traffic away from their own sites to an unaffiliated site. Then mangadex ends up becoming a pariah in that community.
I do see the value in preserving translations, but there was talk over on Novel Updates about a system being developed on their end for handling mirroring of translations that are no longer available due to blog deletion and the like. Therefore I feel that having mangadex also do it is in a way redundant, and while redundancy is a good thing, in this case its outside the scope of the mangadex project.
Basically, what I'm saying is "Don't let mangadex become the mangafox for novels".
As an aside, I didn't know that mangadex had a dark theme until today, so thanks for that.