NBCU technically doesn't have a CEO right now (all top execs report to Comcast President Mike Cavanaugh), so should that particular merger happen, Zaslav would theoretically be in plum position for the CEO role.
That having been said, Zaslav has underdelivered on his promises (he continually missed EBITDA targets the whole of last year) and there's rumors that his benefactors are losing some patience with him, so who knows. Regardless, a potential merger leaves Comcast pulling the strings, so he might end up on a short leash either way.