So you sell your Bitcoins and get either USD or EUR. Now invest, get 80% profit in let say 3 ( three ) months, then 80% profit change to Bitcoin back, and yes you have previous BTC in cash plus new Bitcoins too.
You can also reinvest cash oncemore and get more 80% BTC.
Thanks forum members for previous inputs, if you do not agree that Bitcoin price will drop, just wait for it. Simple. 
Not disagree with your idea. We are in Speculation thread after all.
But still, a simple analysis came from your own instincts without supporting details.
If that's work for you then good.
Best of luck then.
