Who will be the Noblesse after the current one dies? When Kadis Etzamal di Raizel dies, who will take his position? I haven't found references for the Noblesse before Rai nor who will be his successor. Isn't there any information available?
As mentioned by Frankenstein before, there is only one Noblesse. Also during the entire manga up till today (2016-04-15), Noblesse is always mentioned as "the" Noblesse, never "a" Noblesse like is the case with Lord. For example, in chapter 389 where Raskreia was mentioned as "a Lord". This means that there is and was only one Noblesse, and that would be Rai.

Therefore, we can't possibly tell who will be called as "the Noblesse" suppose that Rai dies, since we currently has no information on the succession pattern of the "Noblesse" title like we had on the "Lord" title.