The question is, would you still be alive after 20 years? Life can always be uncertain, although we always advocate for long term and preparing for the future, but in situation like this, its always best to claim your $1 million dollars immediately so you can start maximizing the best opportunities in life, than to get it in installment, in 20 years everything is still unfold.
There may be no guarantees that you can change your life successfully, but with proper guidance on managing your winning amount and strict discipline not to return it into gambling, you will secure a financially stable life without going through financial struggles in the next years to come.
Just wondering if it's fear of financial mismanagement that led to such decision. Under such situation (win) many people always end up in few times with empty pocket, seeing them you won't believe they ever had such amount of money in their bank statement.