Didn't somebody research this, and conclude it would be impracticable for Trump to get on the ballot as a third party candidate in most places, if he decides next Spring that securing the Pub nomination is impracticable for him?
I think the filing deadlines for independents would start kicking in in early March (if there's deadlines for independent candidates earlier than that, there's Supreme Court precedent to challenge them as unconstitutional). But as a practical matter that means you'd ideally want petition drives going on in a number of states earlier than that. Plus you start running into sore loser laws, so by Super Tuesday you've already got problems in IA, NH, SC, NV, etc. Waiting until after Super Tuesday is almost certainly too late. Could Trump drop out immediately after new New Hampshire and still get on the ballot in most of the country as an independent?
Theoretically yes, but it would cost an exorbitant amount of money.
