The big question is who becomes the next emperor. John IV is 15, nearly an adult, but he's blind. Michael VIII's sons are even younger - Andronicus is 6 and Constantine is 4. Alexios Strategopoulos , the man who actually conquered Constantinople, is a prisoner in Epirus.
The last Latin Emperor, Baldwin II almost got support from Charles of Anjou for a bid to retake Constantinople in OTL. In TTL they might actually try for it.
OTOH, Michael had a brother John, who won the Battle of Pelagonia in 1259. If I'm reading is
http://genealogy.euweb.cz/byzant/byzant8.html correctly, he lived until 1274, so he might have worked as a regent for his brother's son or seized the throne for himself.