As for getting your soul back, I've always viewed a Warlock as distinct from Clerics. They don't get their power from their Patron, their Patron is teaching them dark magic. In other words, what you've learned, you will know forever. If you ever break your contract with the Patron, they simply don't teach you anymore. That would mean no more levels in Warlock, but you keep what you've already learned.
So, going sorcerer here would make sense, though story wise being a Sorcerer isn't exactly something you choose, it's something you are. So, if your character learns, while still a Warlock, that he has dragon ancestry or something, then maybe being a Warlock unlocks that inner power. You can even fluff it that this is why the Patron chose to work with you, and why you were able to learn the Warlock powers.
So, going sorcerer here would make sense, though story wise being a Sorcerer isn't exactly something you choose, it's something you are. So, if your character learns, while still a Warlock, that he has dragon ancestry or something, then maybe being a Warlock unlocks that inner power. You can even fluff it that this is why the Patron chose to work with you, and why you were able to learn the Warlock powers.