Well, it's certainly wrong to suggest that no one would have come up with calculus if Newton hadn't: Leibniz came up with calculus at about the same time as Newton.
That doesn't mean that Newton wasn't a pivotal figure in the history of science. Certainly the Principia
was a monumental achievement. But even Newton realized that he was building on the work of previous scientists, stating: "if I have seen farther it is by standing on the shoulders of giants." The work of those scientists in optics, physics, and other fields was available to all; Newton was simply the first to put it all together.
As for the ramifications of the plague, it's an interesting notion. Others, when faced with some type of enforced isolation, often do their best work. Sir Walter Raleigh wrote his "History of the World" while imprisoned in the Tower of London. Hugo Grotius wrote his influential treatise on Dutch law while imprisoned by his political enemies. French historians Fernand Braudel and Marc Bloch both wrote some of their most enduring works while in POW camps.
But to say that the plague was somehow responsible
for Newton's discoveries is an example of reductionist thinking. It is similar to the "nail theory" of history ("for want of a nail . . . the kingdom was lost"), where big events are traced back to their tiniest origins. This type of linear approach to historical causation is, to say the least, simplistic, and ignores too much that also occurred.
Had there been no plague, we can speculate on the possibility of a Newtonian revolution; but then, we can make the same speculation about anything in Newton's life. For instance, if he had been a happily married bourgeois gentleman, instead of a life-long unmarried virgin
, would he have written the Principia
? And if his virginal life liberated him from mundane concerns and thus gave him the freedom to make his scientific discoveries, could we not, with equal justification, say that a girl who dumped him when he was a teenager led directly to the theory of gravity?