We can never tell when the bitcoin will long last but as of now bitcoin has continuing decreasing his value but thats not the reason why we think that will btcoin will survive because this is not the first time that bitcoin suffer in this kind of problem about decreasing his value. Many times that happer but bitcoin manage then properly and pefectly. As a bitcoiner i will support bitcoin till the last.
Much has happened since it appeared in 2009. The issue of legality, scam, etc. has a major effect on bitcoin. But, look at the price movement. Does not it show a significant increase? So, I'm sure, bitcoin will continue to exist.