What alliances might he make and which daughters would he marry to who? Perhaps into Spain or Austria?
I discussed this with
@VVD0D95 a few years ago that "basically" the way to "ensure" this is to kill Friedrich Christian of Saxony in infancy. His mom wanted him to either abdicate his rights to the throne (and retire to a monastery) or only inherit Saxony, leaving Poland to her "favourite", Prince Xaver. When the topic of the dauphin's second wife was broached with Saxony, there was a suggestion of a double match (much like there had been with Spain): the dauphin would marry Maria Josepha, and Prince Xaver would marry Madame Adélaïde (conditional on Friedrich Christian renouncing his rights to Poland so Xaver could be king). Friedrich Christian refused and the idea died in the water.
The schema that we came up with:
Louise Élisabeth to her OTL husband
Henriette to a restored Bonnie Prince Charlie
Adélaïde either to Xaver of Saxony (if his brother dies) or Max III Joseph of Bavaria (if Friedrich Christian doesn't)
Victoire to Max III of Bavaria (if Adélaïde doesn't marry him) or Xaver of Saxony
Sophie is a bit of a wild card that ICR where we decided she ended up
Course, there are other combinations as well:
Barbara of Portugal dies earlier, and Henriette marries Fernando VI like her sister was intriguing
Maria Teresa Cybo's Savoiard husband isn't killed, so Ercole III needs a different wife
Maria Antonietta of Spain marries Friedrich Christian/Xaver of Saxony, so the duke of Savoy needs a new wife
Elisabeth Auguste of Sulzbach dies in childbed with a wedding night baby, so Karl Theodor needs a new wife
The duke of Württemberg's mother (Auguste of Thurn und Taxis) accomplishes it that Maria Theresia backs the duke's sister as an Austrian proxy for either the dauphin or some French prince du sang, and one of Louis XV's daughters winds up in Stuttgart instead*
*we discussed this when looking for a second wife for Bonnie Prince Charlie after Henriette died, that Frederick the Great would likely offer his sister (Anna Amalie) or his niece (Elisabeth of Bayreuth) as a potential wife for Charlie like he did OTL. In which case, if Maria Theresia still refuses the duke's request to marry Maria Elisabeth of Austria, Karl Eugen needs a new wife.
Lots of stuff to play with