According to Ajeet Khurana there are several possibilities.
Number 1: It falls out of favor and is replaced.
In this scenario, likely Zero value.
Number 2: It could replace money.
In this scenario add up the value of the world's currencies and divide that number of 21 million and you get the price per bitcoin.
As you can imagine this is a very big number, much higher than current prices.
Number 3: It's value is dependent on the number of transactions and the cost to mine it.
In this scenario it's value increase if interest increases.
To see a bit more about what is mentioned above, check out this link:
Something about his voice is very soothing to me. :)
The big take away from this is that bitcoin could be worth any number of different prices so only invest what you can afford to lose.