-Spoiler warning for everyone not wanting those!-
It depends how you play the mc. I know there's a dwarven character you can miss if you choose the wrong reward for a quest. You can also miss an Elven character by just not talking to her after your initial meeting. I believe you can get one of two other Elves killed during one of the quest lines, but I've never done it. Twig you currently cant save, but will be able to later. If you choose the wrong option with Cynthia then she stops talking to you, the same can be done with Zenalith, or you can just starve her to death on one of her routes. Last skippable one I can think of is Thea, you basically just choose to leave, or watch her get assaulted and murdered instead of rescuing her.