But, the vitality of Bitcoin is maintained by the continuous mining of Bitcoin. On an average these mining costs are USD 3000 to 3500 approximately. So, what happens when Bitcoin falls to that level?
nonsense. if anything the cost of mining is about $6000 which has been calculated by silly speculators. but in reality cost of mining will always remain near bitcoin's current price because that is how mining and difficulty works.
if price goes up there will be more miners, more hashrate, higher difficulty, less profit, "higher cost of mining". and if price go es down it will be the opposite.
that's why these theories about mining cost are so silly. if difficulty goes up too fast, the more marginal miners will only mine at a loss for so long before shutting down. then difficulty adjusts downwards. it doesn't matter what it costs to mine BTC, because it can always cost less (or more).
if a miner is mining at a loss, why wouldn't they shut down? they can buy BTC instead wasting money on electricity, if they're so bullish.