Well, this adventuress happened 5 years into his abdication when he was a lonely desperate man living in abbey near Paris. So maybe he was into some company.
Austria doing better in Transylvania, however, might be just enough of a push to reconsider his plans and to marry his wife's niece himself, without declaring her husband his successor.
He can also go with Plan A of his late wife and officially name Charles-Paris de Longueville his heir, arranging the marriage of him to his wife's niece and all this. I think this is more plausible, as he was a former cardinal and was not into remarrying his wife's niece.
Inviting over an official successor, though, is very another thing. Also gets rid of incompetent Michael Wiśniowiecki who got crown only because his dad was great general (same goes for Duc d'Engien, though).
In short, there were four major pretenders:
1. Charles-Paris de Longueville. Favored by Queen, but sadly lost first election and was dead by the time of second.
2. Henri-Jules de Bourbon-Conde, Duc d'Engien. Second best Queen's favorite, incompetent and mentally unstable.
3. Michael Wiśniowiecki- homebrew version of the above minus clinical lycantropy, favored as Polish candidate, but a bad stand-in for the King to be honest. Won elections in OTL.
4. The most exotic candidate - Tsesarevich-Successor Alexei Alexeevich of Russia. Tsar Alexis Mikhailovich seriously groomed his older sons (Alexei and Feodor) for Polish throne, they were fluent in Polish and Latin and were educated by tutors from Commonwealth. The idea failed due to Tsesarevich having to convert to Greek Catholic faith (at the very least) and thus formally renounce his rights to throne of Russia to be eligible to marry to Queen's niece and become the next King of Commonwealth. Then Alexei died in 1670 of unknown causes and idea was abandoned by default.
The idea of established successor sounds nicer to me than remarriage. There was no such thing as regency in elective monarchy of Poland. So since any child from second marriage is bound to be a minor when King dies, the Commonwealth might get roughly the same deal as OTL with one more pretender thrown in.