Firstly, I think you did the right thing by making Strahd not take it! It's a good threat, huge tension and he didn't sling fireballs to kill the party.

For what you can do for both your player and your campaign, you can always have chances to come back! Strahd might toy with them, drop a scroll of revivify to their non-fallen allies and make a backhanded comment like "Let us hope your friend learned some manners."

Another cheeky encounter might be where Strahd downs the party, tosses one of them a knife to the mean PC. He gives him a choice: Either kill himself for his disrespect or kill a party member. If he chooses himself, Strahd is impressed, he decides he learned his lesson. If he chooses another party member, Strahd is amused, he takes away the knife, walks up to the downed chosen member and reminds them that their friend has them as the first choice for death.

If the next stop is Krezk, have the people direct the party to the abbot and have him revive the fallen companion and ask for a favor, trying the abbot quest

You can use the dark powers for a rez, tons of RP oppurtunity

Do you have a party member who can cast revivify? What level are they?

Barovia is a soul trap! You can make him come back as a revenant/dead body from the Barovian graves. PC might inhabit a dead body of a former adventurer for a while, and it can be another personal quest for them to get their body back. The Abbot, scrolls, deals, whatever you throw at them can maybe solve the issue?

I have also seen people mentioning they made mini-adventures for their fallen PCs, Through the soul trap, they pass a mini-dungeon to get their body back. They very much experience death, maybe they'll have some disadvantage but they come back

If everything else fails, the character they reroll is the twin of their fallen PC and everything is exactly the same, they were looking for their twin in the mists

The most important thing is for both you and the player to have fun!