You seem to think that Harvard divesting from fossil fuels will cause companies like Exxon-Mobil to collapse overnight.
This is largely a symbolic action. If many other institutional investors follow suit, it's *still* not going to stop companies from pumping natural gas out of their wells, any more than divesting in gold mining would cause gold mines to stop taking gold out of the ground. The last thing a troubled business would do is starve a cash cow.
What divestiture *might* do, in the most wildly optimistic scenario imaginable, is divert a *tiny* fraction of the world's investment in developing new energy stocks toward renewables. Were that to lead eventually to electricity shortages, the price of fossil fuels would automatically rise. That would attract plenty of new investment. A modest rise in prices would swamp any conceivable stock price effect of divestiture, even if all the universities in the world did this.
Finally, as an MIT alum who's taken courses at Harvard, people who manage to land a professorship at the country's oldest and most prestigious university are usually pretty damned smart. That doesn't mean "always right", but it does mean that they probably understand the practical effects of such a move better than you apparently do. This is a university that has managed to build the largest endowment of any educational institution in the world: over 32 *billion*. If that were *market capitalization*, it'd put them on S&P's list of the 100 largest companies in the world. Halliburton's only worth 30 billion.