it's been stated by the new Lead Writer that Malgus is dead for all intents and purposes. he even referenced the Wookiepedia link the poster below you talked about with Malgus escaping to the Unknown Regions as false and was laughing the whole time talking about it because he didn't know where people got that idea from. However, he did drop some hints that Malgus' apprentice is still out there and probably less than pleased that we offed Malgus.
She is set to co-star in the new SWTOR book, so maybe that will be a lead into a new iconic character for us...or just a new loot pinata if she survives the book. Just to kind of increase her aura of BAMF-ery, shes also in command of the Ascendant Spear.