This is a stupid question...will they use the dub work already existing or redo all of it?
I assume you mean the dub track for Slayers and in this case there is no dub track. Slayers Revolution premiered just this past fall in Japan and concludes with the second half starting next month. This will be the first time that anyone other than CPM has handled the Slayers franchise so it will be curious to see what happens.
Btw, the rumor mill for the final two announcements seem to be betting on Soul Eater and Eva 1.0 being the last two to be revealed.