I think Trump can win as a third party candidate. The election will go to the House of Reps to decide. Don’t underestimate the MAGA vote. Pig faced Rove and his ilk need a reality test.
What you're referring to is the MTGA (Make Trump Great Again) vote, which is different than the MAGA movement, which is bigger than Trump. Reagan first coined the term MAGA, for example.
The only 3rd party candidate who would have any chance whatsoever would have to be someone who drew equally from both parties, which Trump has zero chance of doing, especially in the House of Representatives. The only thing Trump would accomplish is destroying the Republican Party and guaranteeing Democratic rule indefinitely. But, like you, he may be willing to risk it.