No, you're not going to donate the money to save people's lives. You're going to use it for your own happiness. And anyway, a million dollars will not do enough medical research to save the lives of a million people. Sheesh.
If you said you would push the button, then you are also saying that you would understand if someone else would push that button. And you would accept that choice as the correct choice to make. Even if you (or your sister, or brother, or child, or mother, or father) were designated the person to die. "Oh, well, sure I loved my son. But the guy had the chance for a free million dollars. Of course he's going to push that button. I don't harbor any bad feelings against him."
This is a really easy one. Which is more important, life or extra spending money?
Having extra money won't make you much happier anyway. People with millions of dollars are not happier than those without it. Happiness does not come from money. Tales of rich kids who are miserable, suicidal, depressed, etc., are a dime a dozen. Happiness comes from doing things that challenge you and interest you.
The first extra million might make your life a little happier. Every extra million above that would do zip for your overall level of happiness.
If you're willing to kill 100 or 1000 people who have no connection with you, just to advance your own selfish interests, you're really no better than the terrorists who flew airplanes into the World Trade Center. If anything, you're worse. At least those people had some cause they believed in that was bigger and more important than themselves and their own spending money.