For the sake of clarity, although some people may think it's pedantic:
1) I should point out I never mentioned anything about a third party in the above quotation. I talked about people voting for a candidate other than Hillary or Trump (assuming they're the nominees), but that could happen in context of people voting for multiple different parties. Third, fourth, fifth parties, etc.
2) Also, whether it's actually a good or bad idea to cast a "wasted vote" is a separate question (and I did say it's "(maybe) arguable" so I'm personally not committed to the idea). As I mentioned above, it depends on one's personal criteria and priorities in voting (among other factors).
3) There's a distinction between what parties want vs. what will happen. For example I've seen articles suggesting if Trump wins the GOP nomination, then the GOP is done as a party. Personally, I don't know how likely this is to actually happen. Maybe it won't happen. However, some people seem to think it's a possibility. If for the sake of argument it's true the GOP will die if Trump is the nominee, then presumably a new party could possibly emerge to take its place. If that happens, I presume that'd be a new second party, not third.