The reign of the Yongle Emperor, also called Zhu Di, Prince of Yan, can be seen as a second founding of the Ming Dynasty in China. However, what if he didn't become Emperor? There are several ways this could have happened; perhaps if the forces the Jianwen Emperor defeat Zhu Di's forces, or perhaps Zhu Di just dies much earlier.
The Jianwen Emperor was reportedly more humane and Confucian than his father or uncle. I therefore doubt that he would do what several things Yongle did, such as dispatching the Treasure Ships under Zheng He, moving the capital from Nanjing to Beijing, and invading Vietnam. I could imagine Jianwen still embarking on the massive public works projects, like repairing the Grand Canal, but not necessarily. Also possible, I imagine Jianwen would still try to weaken or remove his uncles who held military commands (the act which had caused his downfall).
Any other thoughts on how China would look if the Jianwen Emperor wasn't replaced by the Yongle Emperor?