4
Mathlann, the old Mathlann is dead as per GW. They've said it multiple times the old Gods were all eaten by Chaos. Vetock tells us that Khaine was killed (https://youtu.be/RwzsAAdK10s?t=4m25s). Phil Kelly said the same in the WHTV twitch piece on eth DoK lore in fact he said all eth old gods were dead.
Now, yes it would be cool if a new Mathlann arrived. Or if they found a way to have a resurrected Mathlann, but as of now he's dead.