Loot the castle and Strahd will simply kill the PC. He will stop playing with them. A noble does not like to be robbed. I would throw a few encounters spaced between 3 to 5 minutes each. Each encounters in ascending order of difficulty. After 8 such encounters, Strahd appears.
Strahd: "Getting tired yet, guests? You know, a guest does not steal from his host. You behave badly, now, would you care to comeback to the castle and put everything in place. You know, I can keep this up all night long. You will either play by my rules, or become my next minions. You will not rest. You will not win. You will be here forever. That is unless you decide to behave. I am a generous man. You have this one last chance. I give you one minute to start coming back to the castle. I have a wedding to attend. The bride is waiting, but I need a good audience you know. And you will be there. Alive or not. Your choice!"
And if they still do not come, I'd send them waves after waves of difficult to deadly encounters with Strahd safely in the back. They would die, a total TPK. You don't mess with a lord of a domain of dread. You play by his rules or at least, you try to appear to play by his rules.