FormerlyHemlock
Hero
So we have 2 options:
- He dies easily in a pair of rounds of direct confrontation, if the players make their saves he could die practically without causing any damage as some DMs have reported. Players will be happy but tell you the villain was awful.
- He is invincible, your player characters die or go home bored, your players know how worthy were all those roleplaying sessions and reward the DM raising their middle finger.
Option #3: players do something clever.
For example, if they have found the Sunsword, they can keep the Sunsword hidden, perhaps by casting a Seeming spell that scrambles all the PCs' appearances to make the burly fighters look like scrawny wizards and vice versa. Then they go looking for Strahd, and when Strahd attacks a scrawny wizard (really a burly fighter, hopefully one with the Sunsword), the scrawny wizard (burly fighter) whips out the sunsword and grapples Strahd (probably pins him prone too), with Strahd making his checks at disadvantage because of sunlight. Uh-oh, now he can't use his legendary action to escape because his speed is zero, and his attacks are at disadvantage! Another PC now casts Wall of Force around Strahd + front-liner PCs in a force bubble that will keep him from escaping. Now the front liners fight Strahd, at advantage, and he is slamming them as hard as he can with his Legendary actions but... to no avail. And Strahd dies.
And the players feel awesome, because Strahd died, but not easily. They won!
Some people like to win because they are smart and skilled players. Others like to win because their PCs have high stats. Strahd is better for the former kind of group because the latter kind of player will just get frustrated at losing.