Lestilaut is the next Aub Dunkelfelger, there's no way he's going to became even a first husband to an archduchess, much less second or third.

Hildebrand can still circle the small shrines, since they are specifically made for people not omni-elemental. The question is, whether the small shrines have a similar effect on the schtappe as the large shrines do. Because if they do, getting the feystone from all 84 shrines to the subordinate gods should boost his schtappe's capacity quite considerably.

He also knows at least a little ancient language, so it's not out of the question they might have him help in the underground archive, and allow him to visit the smaller shrines in exchange, even before enrolling at the academy. Assuming they still need to translate anything from the underground archive. With the magic tool Grutrissheit being written out on 300 pages of physical paper, I doubt it would also contain the full knowledge of all dead royals, archnobles and high-capacity mednobles, plus potentially a couple of devouring commoners since the beginning of the country, so keeping up the translating efforts seems sensible. At least until Eglantine can finish getting a true Grutrissheit herself, as she swore.

But what's going to happen to Letizia now? Since she's no longer absolutely needed in not-anymore-Ahrensbach, she could return to her family, if Aub Drewanchel allows it. Alternatively Rozemyne and Ferdinand could adopt her I suppose, but with her having a normal archduke candidate mana capacity, if Rozemyne ever has a child, male or female, chances are, that child will have a considerably higher capacity and thus be near guaranteed to become the successor.

I guess if Letizia and Hildebrand's engagement was not written out in terms of positions like Adolphine's engagement was, she could marry into Werkestock and become Hildebrand's first wife over there. With Hildebrand being the only one of Trauerqual's children who isn't an Aub somewhere else, he's the default choice to succeed his father as Aub Werkeshock, even if his schtappe can't be fixed, unless Trauerqual adopts someone. But with the kind of wringer the boy was put through already, Trauerqual is probably a least a bit reluctant to take yet something else away from him.

I suppose with the next book series turning around Hannelore, there's always the chance she will marry into Werkestock to become Hildebrand's first wife... though I'm still holding out a little hope that she'll somehow be able to marry Wilfried, as she seemed quite happy to do, until their brief engagement was quickly voided again. It'll be a hard sell for the only daughter of Aub Dunkelfelger and his first wife to marry someone who won't become an Aub, but it's not entirely impossible.