2) Yes, but I'd happily vote Green Party while sharing nearly nothing in common with their politics if I could be absolutely certain that neither Trump nor Hillary were in danger of being elected.
But others would vote libertarian. In the end a Democrat or Republican would win because of their die-hard base would be enough to take it with everyone else split between 2-3 parties.
3) It very well might, but for an entire generation both major parties would be on notice. (If the schism didn't destroy one entirely)
Their solution would be to make it all but impossible for third parties to get on the ballot, then add a few more hoops people must jump through to actually get to vote, stuff like fewer voting locations, with fewer staff to help out, more stringent identification requirements, or fewer opportunities to vote absentee. Sounds familiar doesn't it?
Most people will not put much effort into going to vote if they are not really enthused with the candidates they are voting for, and that is the exact scenario you are talking about, people voting for a third party they don't really agree with just because they want to stick it to the primary parties. Every little bit more effort required will have dramatic results in stopping people from doing just that.