i thing it's never happen. because in the world same of people using this Digital currency. so if every one will be not using this Digital currency in the world then this will happen (goes zero). 

it's Natural. BTC value is depend on Investment and how much interesting to buy this coin.  so BTC price going down is good to New Cripto-currency investor. because new ones can invest less money and start this Cripto-currency field.

no. in this days BTC has a Little bit drop. but still 1 bitcoin = near 10000 US doller
and this day introduces more coin type. but still that new coin values also depend on BTC. most people try to so heard mining BTC using many different ways and also more people spend lot of money to take a BTC. so i don't think BTC popularity is going lower.    

it's normal behavior. every coin has a drops. so i think it's temporary issue. 

BTC is depend on it market supply and it demand. as a example today 1BTC = 10976 US dollar , 1BTC = Euro 8852 .... etc
so this currency rate change regularly.  

yes i think so. because now many investors invest this industry (cryptocurrency Industry) 

BTC mining is a energy wasting process. so if we used solar power or any other sustainable energy sours to mining BTC it's more good for our environment.