This was covered several chapters ago. No, her dying is bad.
Something-something about power collapse within the kingdom... other kingdoms then eyeing the weakened one, and Char's life would still be in danger, as she would be targeted by those opposing kingdoms instead of Giselotte.
The story is the royal birthmark. He has the mark of royalty on his chest. And the rest can all be inferred from the fact he was raised by people who "found" him.
A bit hard to answer, since she's had like 3 forms so far...
If it helps jog your memory, she's the demon maid turned demon child turned demon child that forgot she was a demon by the principal. Chapter 75 was the when we got introduced to her in child form and we get introduced to her original demon maid form in chapter 47