Abiy was the compromise candidate favored by the IC and he was less polarizing, unlike Lemma. He was palatable to the Oromo because the Oromo masses thought he was one of them, and Amhara extremists believed they could manipulate. The Tigray was simply told to behave.
The IC will definitely try to keep Ethiopia together. But unlike the Ethiopia of the past, what we have today is a highly polarized population, the rise of ethnonationalism with defined regional borders, and well-armed paramilitary troops. The center is losing power every day and the periphery is getting stronger.
Abiy or any future leader cannot take the country back to a centralized system of governance and the current ethnic federalism will lead to further division and aspirations for complete autonomy or outright independence.
I don't see Ethiopia adopting true federalism as we understand in other countries; the choice comes to heavily centralized state or ethnic federalism with even more autonomy.
Even some in Western circles are beginning to imagine disintegrated Ethiopia.