Its not just gabe's thoughts that matter- Many startup founders forget that as you have people who work for you. He has a responsibility to the people working for him- If he gets a offer for some ludicrous amount, does he not owe it to his staff to do whats best for them? Im sure most of the staff would be happier with a few million bucks than not.
And what if MS says "We want to buy you, we promise we wont touch you and will sign these docs to ensure you can keep doing things your way" - At that point, its not about morals, its about the fact that not doing something like that isnt fair to those people in the companies who are not yet millionaires, like Newell already is.
In short, if Newell could guarantee that the company would have no changes moving forward and could also get significant wind falls for all his staff, then yes- I expect him to sell. Anything less would be not prudent.
* Nobody knows if MS would be willing to pay as much as would be required to have a outcome like above. I just think that Valve is in the #1 or #2 spot for "Companies we want to buy" at redmond.