He can't win a GE on his own. He would effectively have to start another party and put candidates in every seat. He wouldn't have the party infrastructure that he's had previously and frankly he's too lazy to put in the hard work involved. He would also have to have a hell of a lot of money, and I doubt that there are many donors batshit enough to be willing to bankroll him.
Mind you, he would split the Conservative vote and let Labour in, so maybe he should be encouraged.