So while reading King over the Water by Alice Shields and Andrew Lang, I came across a very interesting passage. Twice, in 1697 and apparently in 1700/1701, William III offered to adopt his brother-in-law the Prince of Wales as his heir, in exchange for undisturbed possession of the throne during his (William's lifetime). This offer is repeated in several books, including Ungrateful Daughters, the Old Chevalier and A Court in Exile, so clearly this offer was indeed made. The fact that William, the Protestant hero, dropped any demand for the Prince to become Protestant makes the fact that James II and Queen Mary rejected the offer even more ridiculous. So lets say the offer was accepted, either by Louis XIV accepting on behalf of the Prince or by James finally making a good decision.
What happens next? How would William, assuming the offer is genuine (which I believe it was. After all, if the Jacobites and French had decided to publish the offer it would have done more damage to William than themselves) go about enforcing the agreement? Would knowing that his surrogate grandson's accession was basically guaranteed change the way Louis XIV acted in regard to the Duc d'Anjou's inheritance? Would the Spanish succession war still break out? What about the British isles? Would we see a return of the Crown's full authority? Would a union between England and Scotland still occur?