European stocks plunging 20 percent. Junk credit spreads widening past 2020 crisis levels. The euro sinking to just 90 cents. The predictions for financial markets are ominous if Russia cuts off its gas supply to Europe.

Gas shipments are currently running at reduced levels, with the main pipeline shut for maintenance for 10 days, and fears are building over whether Moscow will turn the tap back on. Many investors are asking: How bad could this get?

To answer that question, strategists from across Wall Street have tried to put numbers on a scenario that would be unthinkable in normal times. There are so many variables—such as the length of the prospective shutdown, the extent of supply cuts, and how far countries would go to ration energy—that anyone's prediction is a guess at best.