The Rough from D1 was corrupted and became Blood Raven in D2, this is certain.
Though I read somewhere that the Summoner in Arcane Sanctuary was the Sorcerer from D1 supposedly, this might be before the story lore was reconstructed to what it is nowadays, or just my mistake.
Since storywise 20 years ago the three prime evils were defeated by a group of heroes(I presume 7 of them?), where are they now? Should we suppose they were hardcore characters and eventually one accident happened? It was nice to see the Necromancer's student and heard about him. What about the rest specifically? Such strong and unique individuals couldn't be unsung and impromenent by now and for so long.