is bitcoin possible to stay forever
Why not man. Look at the popularity of the bitcoin, its going off the chart and more and more people are getting into bitcoin trades everyday and every single minute. Im sure that this upward trend of investment will keep happening until we see no one has left that is not invested into it. Yeah thats really possible. Because some people will start believing in it when the price will reach to 15K and some of them might trust it when it reaches 20K and so on. Until the market gets fully capped people will keep coming and the aint gonna stop. So yeah I'm pretty sure that bitcoin will be there forever. 
Lokk at the market capitalism of the bitcoin . The market has crossed most valuable assets in the world already and thats why government will also try to go into it soon. This will bring more regulated bitcoin and thus people will start coming into it ever and ever. Thats the oxygen for the bitcoin and it will never die really.