During the time Timur was rampaging in Anatolia, the Ventians and Genose saved the Ottoman army by ferrying them to Thrace, for they preferred the Ottomans to the Timurid's. However, what if this ferrying never happened, and the Ottoman Army was completely destroyed in Anatolia, and the Ottomans only had their European possessions?
I mean, given the desperation of the situation I can't imagine that there are literally
no boats on the Asiatic shore which the Ottomans can use to ferry themselves across. Surely there are boats in Smyrna, Antalya or any of the Anatolian ports the beaten Turks could have retreated to?
I would argue that the Venetian/Genoese story is just an anecdote, rather than a 100% account of what happened.
But let's assume that the Venetians/Genoese turn hostile at this point or something and the Ottomans Army literally is stuck in Anatolia and destroyed. If we look at what happened OTL the Ottoman Interregnum consisted of contenders in Edirne (Suleyman), Bursa (Isa) and Amasya (Mehmed), two of which were in Anatolia. Already in 1403 Isa and Mehmed were fighting each other for the throne in Anatolia, so that indicates that the rulers were still able to raise soldiers/mercenaries to fight for them, and that Ottoman power was not completely wrecked after Ankara.
This is not even to mention Ottoman Europe, which funded enough troops during the Interregnum to pose a very serious threat to Mehmed I.
But let's assume again that the Ottomans get totally wrecked in Asia and they lose all their Anatolian possessions. Then for succession purposes, Suleyman would almost certainly become the next Sultan, given that he ruled the European part of the Empire at the time.
From his OTL actions, it doesn't seem like Suleyman was a very energetic Sultan (of course this might just be propaganda), so the most likely result is dethronement by one of his brothers (probably Mehmed). If not, I could see the Ottoman Empire being quite peaceful with its neighbors during his reign, though I suppose there's a high chance that Suleyman will attempt to retake the lands ceded to Byzantium for his throne.