By definition, it has already begun, because cyber attacks are considered an act of war.
And the shooting down of the drone was also an act of war.

There is a lot of talk about the Iranian bomb that has not yet been completed. In fact, however, Iran already has another, more effective option: it can block the Gulf of Hormus or at least considerably impede shipping. The "oil flow" thus reduced leads to higher oil prices, which in turn chokes off economic development. Experts are discussing an oil price of up to $300 per barrel. That would, of course, be the kiln off, real and symbolic.

The global economy and the bloated banking madness are already in the red anyway. A rise of the oil price above 100 $ per barrel is enough to lead to quite considerable shifts.

So Trump did not whistle back the attack because of feared collateral damage, but because of the imponderable risks for the financial system.