Could a Trump nomination cause an exodus of moderate Republicans?

[Indy Texas]

I could see someone like Susan Collins endorse Hillary Clinton and announce she's becoming a Democrat.

If I were her, I'd say I'm not voting for Trump and leave it at that.

Then, after election day, if the Democrats have a majority, I'd say I'm becoming an independent and caucusing with the Democrats. If it's a 50-50 tie, I'd say I'm becoming an independent but haven't decided who I'll caucus with. If the Democrats don't take back the Senate, I'd leave things the way they are.