Well, this is the easiest question to answer; and in fact we have answered this question countless times here and elsewhere.
The leadership style he has adapted, that of 'one-man show' will ensure that every bit of his legacy crumbles the moment he is out of power.
Take one example, the popular fight against corruption. He has fought it by sheer force; no support mechanisms that will ensure people would have internalized the fight in a way that would support the fight. There are no reward mechanisms, only intimidation is relied upon a a means that will deliver results.
Guess what, even now, people have devised ways of doing their thing, intimidation notwithstanding.
In short, what ever Magufuli is doing has no sustainability beyond his leadership.
His only legacy will be of physical structures, roads, bridges, Stieglers gorge, Dodoma and so forth.
In short, his leadership has no philosophical articulation. No ideas/thought about anything concerning his leadershi.
However, biggest leadership failure that will always be around him is his antagonistic, forceful approach that is leading to the loss of our national cohesion. This will be a big disappointment for many who had started of with optimism about his leadership..
Now he is proving daily that he is incapable of uniting the people of this great nation.
Sooner or later, he will be relying solely on state power to keep him in office.