You are right; I cannot say for certain that someone else would have solved the nitrogen fixing problem in time to save humanity from global starvation, but for it not to happen, it would have required a lot of chemists to all not perform the sort of experiments that chemists are trained, employed and choose to do.

Having read somewhat widely, as a kid, about the history of technology, I was struck by how often several people were working independently on the same ideas at the same time, but that is not so surprising once you realize that the timing is often determined by when some prerequisite knowledge became available, or some prerequisite capability was mastered. Einstein stands among the most original thinkers of all time, but even he was standing on the shoulders of people like Heaviside, Fitzgerald and Lorentz (and Maxwell, of course) - yet the first three, at least, are invisible in popular historiography.