Buying and selling bitcoins is useless.
There are reasons why Bitcoin prices go up and down, it may be due to some miner rage, it may be due to some underlying currency price fall, I actually don't care.
I just care about Bitcoin existance, 1 BTC will ever be 1 BTC regardless of Bitcoin prices, none can change that.

for what hold a coin that is not valuable? I am sure that bitcoin already are at stake
and there will probably evolve again. if it has been touched in the price of $1

I think 99% of Bitcoin holders will have bailed out by the time it reaches the $1 floor price, especially if the descent occurs over a long period of time. Only hardcore fans (and of course dreamers) will be left in the game. I estimate chances of a full recovery to be pretty low at this point because Bitcoin's credibility will have been permanently tainted.
Still, I would probably buy 50 - 100 Bitcoins just in case 

Maybe you have some point with that but i could say many wi take this oppurtunity to buy more bitcoin and leave it in their wallet in years as same as what they did for past people who buy bitcoin at cheap price and now became millionaires people will come and buy and buy more because many will believe that bitcoin will bounce back as history said, bitcoin has many downs but still survive in terms of crisis.

no if so many people buy bitcoin and expecting for price rise,the demand will be more than supply which affect the price and it'll rise a lot
that's simple,and i'm sure the price will recover back to ~200$ as people expected from buying a bitcoin

Bitcoin is volatile, extreme volatile. But even fluctuation of bitcoin has its borders. I am convinced that we won't ever see bitcoin price lower than $100 at this point.
There is no way that with our current market cap and all bitcoin startups, companies and services bitcoin price could go as low. If someone is telling you otherwise - he is just being paranoid.

How in this world that bitcoin could dropped to $1 dollar ? If this really happen, that must be a big serious problem about bitcoin and i don't think bitcoin will raise again.  So basically it's worthless

There's a little possibility in the far future that an alt coin will replace bitcoin. We might not see it right now but there's still a chance that it happens.

Once bitcoin dropped its price to 1$ from 440$, then that simply means that people are dumping all their bitcoins and are switching to another crypto-currency. I might as well dump my bitcoins at that time before it becomes completely worthless.

It's either an alt coin will replace bitcoin or bitcoin will be stronger than it was.

I will buy as much as I can and keep my fingers crossed for the return of the Jedi.

I would buy like 50 BTC and store it until price goes to ~$1k