Would it be wrong if one said, 'Either she will leave or I will'?The most common and natural way of saying this is "Either she leaves or I do!"
Yes. I consider the dictionary sentence wrong too.Would it be wrong if one said, 'Either she will leave or I will'?
OK, but what if it's not an ultimatum? What if it's a prediction instead?Yes. I consider the dictionary sentence wrong too.
When giving ultimatums, we typically use this pattern: Either something happens or something happens, with both clauses in the simple present. There's absolutely no reason to use will in either of the clauses in this case. See post #2 for the right way phrasing.
Then that's a completely different meaning, in which case you should use predictive will in both clauses.OK, but what if it's not an ultimatum? What if it's a prediction instead?