Yes, I would agree that the way circumstances panned out in the late fourteenth and early fifteenth centuries, the Byzantine state theoretically had a shot at survival and maybe even reconquest. (The extent of that reconquest was of course not likely to be very great. The real world isn't a game of Europa Universalis.) The fragility of the early Ottoman state, for instance, has been vastly understated. It suffered severe shocks over the succession on multiple occasions and of course had perpetual issues with religious fractures (witness the Kizilbaşi revolt from the end of the fifteenth century - although that's slightly out of the scope of the Byzantine state's OTL survival, it does indicate that pressure along those lines was something to which the Ottoman state was susceptible...and Bedreddinite heterodoxy, which was around earlier on and which did cause problems during the OTL Interregnum, offers a similar point of departure).
The fundamental problem with arguments claiming that the Ottoman state was unstoppable after the mid-fourteenth century (if not earlier) that also claim that the Byzantine state was in terminal "decline" after [insert date e.g. 1071, 1204, 1348] is that those states were drawing on the exact same resource aggregation. Manpower available to the Ottomans had also been and was later available to the Byzantines, and the productivity of the territory under control did not really change, either. Arguments that the Ottomans Would Definitely Win and the Byzantines Would Definitely Lose therefore hinge on theoretical problems with the structure of their states (which were effectively based off of one another anyway) or on the old trite standby of "it happened that way ergo it could not have happened any other way". The possibility theoretically existed for Byzantine military revival into the fifteenth century - it may have been so unlikely as to hardly merit mention, but then again, the Ottoman state had a similar starting point and, from what I remember, did reasonably well.