Malgus himself is unlikely to play any future roles, considering Lead Writer Hall Hood has confirmed that Malgus is dead. If anything, his only known apprentice, Darth Karrid, would continue his path. Then again, the Sith Inquisitor may also do something to similiar extend since he/she also supports the change within the Empire, to what extend that happens is of course up to the player.
As far as "plot devices" go, there is still the Infinite Engine from Revan's complex on Nar Shaddaa. Let's say a powerful Sith Lord (like that ominous Keeper of Mysterious or Darth Nox, who afterall is in charge of the Pyramid of Ancient Knowledge) gets a hold of it and manages to make it grow very fast through some sort of Dark Side ritual, they would have the means to get themselves another Foundry or Star Forge.
Really? I'm sure in that interview he just stated that the stuff on Wookiepedia was false because his fate has not been confirmed yet. He seems far to important a character to just kill off. What's more, doesn't his 'death' seem a bit strange too you, there is a clear game mechanic put in their that means at the end of the battle he always
falls in the pit. You see no body die, no cutscene. What other characters have fallen in pits and come back, Darth Maul, Darth Sidious, Luke Skywalker, hell there's probably some alternate universe where Mace Windu comes back - I highly doubt Malgus is dead, all the signs indicate he isn't. I see him as a candidate for replacing the Sith Emperor.