Short answer: yes, you'll get updates for the foreseeable future.
long answer: you're not technically buying it. You are donating towards the development of the game and are able to access any future content valued at or below the amount you donate. If, for example, the cost increases to 6 million dollars you would no longer have access to new content without donating the higher amount.
(I have no intention to change the price until the game is much further along.)