Those 150 billion will be taxable at the same (hypothetically 30%) tax rate, reducing the expected return by 45bn * 5% chance. The expected return is still negative; all this bet does is shift tax liabilities in time, which admittedly would matter to some people who subscribe to short-termism.
I guess to truly calculate it you need to estimate how long it will take to get the ROI (i.e. reach the point where you need to pay taxes on the 150billion). And add back what you can earn by investing the money you didn't have to pay taxes on. I'm not sure what the magnificent 7 can expect as a ROI on invested money though, given that they tend to have enough cash to invest anyways and just pay out dividends.
