It's possible but who really knows.
ZixZax could reappear as a companion of sorts. Possibly acting like Withers or Volo, being a source of information or utility.
Or we could get an actual companion that's an imp who can aid us in battle (Having a romance arc would probably be a bit weird... But then again, I've seen people thirsting for Sazza...)
Honestly, I could even see a potential for having imps as a playable race. If they do a sort of soft origin for races (I.e. Unique racial prologue) and some unique racial interactions with various factions and NPCs.
But it's really kind of up in the air as far as speculation goes.
Imps are generally well ostracized in Divinity. Their connection to demons, their inhabitation of Nemesis plane (As opposed to Rivellon) and their general savagery make them undesirable to interact with by most races. So it would be easy to justify not including them.
It all comes down to what Larian chooses to do.
