At what pricepoint is bitcoin dead?
What do you mean? Bitcoin survived two years being worth less than a dollar - what makes you think it would die because of a price drop?
For the most part, Bitcoin works just as well at 0.1 USD or 10 USD - difficulty will adapt for the changed mining reward, as it has ever since its conception.
Everybody knew right from the start that mining profitability tends to go towards zero - that's how the system is designed and how the market works. Mining was never supposed to earn people large amounts of money, it's just a pretty clever way to get Bitcoin in circulation and secure the transactions at the same time.
Well unless everybody is doing short sells, I can't see making any money on the trading either really.
I think you really have a serious misconception about a currency. Money is not supposed to earn you money all by itself. Of course you can speculate on anything but that's not what Bitcoin was made for.
Bitcoin will not die because you can't profit from it anymore directly. Start a business with it and be more competitive due to some of its unique features. That's a good way to still profit from Bitcoin - regardless of the price.
Bitcoin is just a sounder form of money - nothing more, nothing less.