The Joker's apparently still dead, but he still haunts the lives of those he's encountered. So…these fights with the Joker are just some very odd hallucinations? Could be wrong here.

Though killed by Superman, the Joker continues to haunt the lives of all those touched by his madness. By destroying Metropolis, he set the events in motion which made enemies of Superman and Batman. If he were alive to see the chaos he'd created, he would surely be smiling.