The problem is this, in the rpg book “the witcher's journal”, the system says that higher vampires can regenerate from any type of damage on their own, and that it's just a matter of time, without even mentioning profound damage like what Regis suffered at the hands of Vilgefortz, or the Manticore's silver, that prevent regeneration without ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.