What can happen with Witcher 3 old pals after the main story?
Well, some old pals might just go their separate ways. For example, Zoltan could head back to his own business, maybe continue with his dwarf gang's activities. They might not be as closely involved in Geralt's life as during the main story.
After the main story, your old pals in Witcher 3 could still have some interactions with Geralt. For instance, Dandelion might still come to Geralt for help or to share some new gossip or song ideas. They could also be involved in side quests that pop up post - main story. These side quests can further develop their relationships with Geralt and add more depth to their characters. Sometimes, they might even offer some unique rewards or information that can be useful in the post - main - story world of Witcher 3.
In the Witcher 3, after the main story, old pals can have different fates. Some might retire to a quieter life. Take Vesemir for example. If he survived the main events, he could be spending his days teaching new Witchers or just enjoying the peace of Kaer Morhen. Others like Triss or Yennefer could be involved in magical research or political affairs depending on how their relationships with Geralt ended. And then there are those like Roche and Thaler who might be involved in their respective military or espionage activities, but still keep in touch with Geralt on occasion.