During the 17th century, specifically at accession of Sultan Ibrahim the Mad, the Sultan was the sole surviving male member of the Ottoman dynasty. What if shortly after Ibrahim took the throne he were to die without any sons, who is the new Sultan. My guess would be someone who is either married to an Ottoman princess or the son of one in order to ensure some continuity of succession but the problem is there were so many people who could fit that criteria. Also, what role would Ibrahim's mother, the very powerful Kosem Sultan play in the succession and future regime?