I just got to Velen. But before, in White orchard, there is something wrong with liberated area and vendors. The small community gets a generic merchant vendor, who vanished from my game and a bunch of peasants, who stay there and work. In statue/altar, people praying and a herbalist spawned and ALL of them vanished from the game... Bug or not? Solution and if yes, how?

The altar was overrun by the wild hunt when you were fleeing from them to wyzima

No, this has to be a bug/glitch. Area's NPC's vanished before i killed the griffin, when i had the herbalist and hunter quests... I found some posts classifying it as an old bug, which mentions area gets bugged after the contract quest (with the wraith in the well), or it erroneously tries to "respawn" like 2 out of the 3 monster nests in the area do, but since the reinhabited area's monsters don't respawn, it gets stuck forever. However, i think one of the patches made the unique alchemy pattern of this herbalist, available to Tomira for sale as well. But still, it is very nerve wracking for npcs to vanish on you. Especially since you got through so much to empty their area...

Did you fast forward time to when the merchant is suppose to be there?
If so, if you're standing on or too close to his spot, he won't appear. If so, move away a bit and fast forward time another 1 or 2 hours and he should be there.
It's something I've noticed a few days ago with Kear Trolde's armorer.

No. Everyone from there vanishes permanently. No meditation no nothing brings them back. The other generic merchant though at 2nd campsite with peasants, with meditation, respawned...