@Serkket
@Doomer
Replacing a Royal Family isn't that easy. In fact, in Europe, it was damn near impossible once the concept of feudalism got entrenched. Aristocratic societies do not generally tend to favour strong, central governments (i.e. an autocratic monarchy/absolute monarchy) because it dilutes their privileges. Thus, they like their Royal Families weak and dependent on feudal/noble lords. A ducal family taking over, while on its face quite logical due to their strength, would actually herald the worst nightmares of many a noble family who enjoy having a weak Royal Family. Even then, it's unclear who should rule should Rovel's family take over: Rovel himself has no overt interest, Ellen is far too young (and also shows no interest), Rovel's mother technically married -into- the family, so she's out, which would leave Sauvel -- and given the current rumours about his failed first marriage and his scandal-ridden second, it's probably not a good idea to enthrone him. Even then, it's unclear whether Sauvel would even want to.
Indeed, for many aristocratic families, the prince-regent's self-destructive behaviour is probably a godsend because it means his political clout will self-destruct on its own short of him backing down and appeasing them.
@JoshuaFord
They just hid it, unfortunately. the Goddess made it clear that the tattoo would remain there indefinitely as a way to remind Aria of her sins. It's just hidden away from others so long as Aria truly repents.