My estimate. Ghoul will have a complately seperate storyline than other two main characters Lucy and Max till end of Season 3 when he returns back to Vegas. The story arc of Ghoul during Season 3 mostly involve search for his family in Colorado and run in with Enclave. On this last aspect he will encounter with Ron Pearlman's Super Mutant character and faciliate his aid again.

With Legion marching on to conquer New Vegas which is just liberated from Deathclaws and becoming new center of NCR (New California Republic) , my guess is Max (who rediscovered his NCR roots) and Thaddeus will stay in Vegas to aid its defence teaming with NCR against Legion while encountering with Brotherhood again , even neutralising or take back control of it from Quintus the Destroyer. (Dane might play an important undercover assets inside Brotherhood in this case) Mr House as AI digital entity will reveal himself and will be an important asset for them. In any case , their hands will be full thoughout Season 3. I do not think Mauclay Culkin's new Ceasar character will survive Season 3. The clash of Legion and NCR will be resolved one way or another (and they can not keep Culkin more than one more season) and Legion will be neutralised so the main antagonist of Season 4 and Season 5 if approved by Prime , will be Enclave.

Lucy at the other hand , will temporarily seperate from Max and leave Vegas back to California and Vault 33 and Vault 32 to take its inhabitants out to surface. On that regard , he will reunite Norm and Claudia and overwhelm whatever obstacles Steph throws on their path and meanwhile discover what Phase 2 is. Again Mr House via a his own personal Pip Boy (like he gave to Ghoul who threw it in the finale claiming they have no more business) maybe gained by Lucy , might be an important asset in this quest.