So on the wiki page of Isabella we have the following:
"In December 1541, perhaps exhausted by her circumstances, Isabella signed an agreement with Archduke Ferdinand: she would abandon Transylvania and take up residence in the Szepes County. However, when Ottomans attacked again, Ferdinand did not have enough military power to defend his territories (see Siege of Esztergom (1543)) and the agreement remained forgotten. Poland proposed to solve the issue with another marriage – Isabella would marry widowed Charles V, Holy Roman Emperor, Archduke Ferdinand, or his eldest son Maximilian. But Ferdinand hoped that he could acquire Transylvania by other means."
Say Ferdinand accepts and is able to manoeuvre this marriage to increase acceptance of his reign in Hungary. John S. Zapolya is compensated and given some properties, raised alongside his cousins/now step siblings in Wien. The Ottomans at the time would soon be distracted by conflict with the Safavids. Do we see political consolidation behind Ferdinand, enough to reclaim parts of Hungary and secure a truce with the Ottomans?
"In December 1541, perhaps exhausted by her circumstances, Isabella signed an agreement with Archduke Ferdinand: she would abandon Transylvania and take up residence in the Szepes County. However, when Ottomans attacked again, Ferdinand did not have enough military power to defend his territories (see Siege of Esztergom (1543)) and the agreement remained forgotten. Poland proposed to solve the issue with another marriage – Isabella would marry widowed Charles V, Holy Roman Emperor, Archduke Ferdinand, or his eldest son Maximilian. But Ferdinand hoped that he could acquire Transylvania by other means."
Say Ferdinand accepts and is able to manoeuvre this marriage to increase acceptance of his reign in Hungary. John S. Zapolya is compensated and given some properties, raised alongside his cousins/now step siblings in Wien. The Ottomans at the time would soon be distracted by conflict with the Safavids. Do we see political consolidation behind Ferdinand, enough to reclaim parts of Hungary and secure a truce with the Ottomans?