Another return of Piasts:
Janusz III (1502-1526) Duke of Mazovia, m. Katarzyna Radziejowska
1) Konrad IV (1525-1557) Duke of Mazovia, m. Zofia Jagiellonka (1522-1575)
1) Bolesław VI (1548-1600) Duke of Mazovia 1557, King of Poland 1572, m. Maria Maximiliana of Bavaria (1552-1614)
2) Zygmunt (1550-1555)
3) Kazimierz/Casimiro (1551-1603) Duke of Bari and Rossano [1] m. Margherita Gonzaga (1564-1618)
4) Katarzyna (1553-1609) m. Albrecht Friedrich (1553-1618) Duke of Prussia
5) Janusz IV (1556-1581) Duke of Mazovia
6) Zofia (1558-1611) m. Henri III (1551-1599) King of France [2]
7) Anna (1562-1624) m. Ferdinand (1529-1595) Archduke of Tyrol
[1] Bona Sforza was not poisoned ITTL and lived longer (maybe she would spend her last years in Mazovia rather than in Italy, with daughter and grandchildren, if she is still conflicted with her son) and passed her Italian inheritance to grandson. Considering the fact, that even Polish Vasas tried to regain her duchies of at least financial compensation it seems likely, that Bona's Piast descendants would be interested in Bari and Rossano too.
[2] Considering the fact, that Elizabeth of Sweden was considered for Henri (at the time, when Vasas were still seen as parvenu dynasty) Zofia of Mazovia is decent choice for Queen of France (and unlike Elizabeth Vasa she is at least Catholic).
@Zygmunt Stary
How do you see development of Piast realm? Jagiellons had hereditary Lithuania, Piasts have hereditary Mazovia (and may have both, as Zygmunt August could make his nephew GDL). Mazovia is not GDL, but still has some advantages: is not in danger of being conquered by Muscovites, and, that is propably the biggest advantage, numerous nobility of Mazovia was regalist and very loyal to their dynasty.