We can't tell you
Balance doesn't come from the monsters you put on the table, it comes from how you play them and how your players play their characters.
If you play Strahd as written, a clever and diabolical opponent with centuries of experience of wiping the floor with adventurers then, unless your players are very, very good and highly experienced then they are dead PCs walking. See How can I play monsters and NPCs up to their potential?
For example, Strahd has these abilities that will make things really tough on the PCs:
Legendary Resistance (3/Day), Regeneration, Spellcasting particularly detect thoughts, animate dead, nondetection, greater invisibility, polymorph, animate objects, scrying), Spider Climb, Charm, Children of the Night (1/day).
Used judiciously, with that on the table, I could kill the party you describe with no trouble at all. Basically, I'd pick them off one by one.
Given the gothic horror nature of the adventure this would be a very nice end to the campaign: just when they feel themselves strong enough to take on the BBEG he teaches them a lesson in hubris and ruthlessness. Classic!
Alternatively, I could put a dozen minions on the table with them., employ them stupidly and give the party an easy win. but that would be boring.
You have the power
Strahd likes to play with his food so it is completely in character for him to devastate the party, gloat and walk away, just so he can do it again tomorrow.
Or weaken the party and then leave them to his minions in a number that you are confident the party can deal with even in their emanciated state.
And here is the little DM secret you need to know. Come closer, I'll whisper it.
Monsters die when you want them to - hit points are a tool but there is nothing to stop you saying "It dies" even if it has a gazillion hit points left.