when there will be no bitcoin remain to mine then the price of bitcoin will increase much more. because the demand will increase and the supply will decrease, therefore i think people will offer more high price for buying bitcoin.
Well, that probably the possible scenario and also, I think sending charges will definite increase All is just a speculation but theres a posibility to happen.
Bitcoin is not threatened I think if mining profits decreased,but if another coin can addressed the some issues which bitcoin encounter like for eg in speed etc then its a game changer.