The best outcome for everyone (but the BBC) is for all three hosts to go to another network and set up shop there. Call the new show anyhthing you like. The magic of Top Gear lies in the hosts, not the network. And Lord Knows, not the BBC.
Top Gear is the most popular TV show in history, with over 350 million viewers worldwide. There is no way in hell the show will fade away. Or the cast. There is no way Clarkson can be replaced, successfully. Fair or not, many viewers would see May and Hammond as traitors. The two will quickly realize they would be insane to stay, especially given their other (much more lucrative) options. So they will go too, probably to rejoin Clarkson at a network of their choosing, where they have *much* better support and artistic freedom. And hot food.
Clarkson was paid a measly $1.5M/year by the BBC. He can make more money per *episode* at a real network. It's plain from his recent shenanigans that Clarkson has been eager to rewrite his contract with the BBC for some time now. The only question is how soon Hammond and May follow Clarkson's example and head for greener pastures.
Bet on it.