Since Marcille’s greatest fear is that she’ll outlive her friends and family (iirc, she already outlived her father), her dream is probably to find a way to make people live as long as herself at minimum. At worst, an undying utopia.
...Could Marcille be the true final boss? After the dark elf jobs out and Marcille seizes power, she’d basically be able to keep everyone she cares about here. Especially Farlyn.