I guess the question is...what is a "bad" night for the GOP, and what is a "disastrous" night?
If they win 30-40 House seats, but lose a net of 2-3 Senate seats and 2-3 governors chairs, what does that quality as? I'm thinking that is where this is going to end up.
I personally think the measure for the GOP is a fine night is winning back both chambers of Congress.
If they don't win the Senate back (either staying at 50 or the Dems gaining seats), then I'd consider that a disappointing night for the Republicans frankly. But I'm also expecting them to win the Senate back so this is also based on my perception of what will happen