Logistically, it might be easier for a character from Fear the Walking Dead to disappear and then reappear much later in time on The Walking Dead.
With The Walking Dead asserting itself as a ratings juggernaut and pop culture phenomenon, AMC in 2015 elected to double-down by launching the sister series Fear the Walking Dead, moving the action from Atlanta and environs to Los Angeles and introducing a whole new group of characters.
AMC has released a teaser image hyping the recently-announced The Walking Dead/Fear the Walking Dead crossover.
Robert Kirkman has promised that Heath will return “eventually,” and speculation is that his return could happen all the way across America in Fear the Walking Dead.