I think it will still be for a long time, as it is first ancestor of crypto currency. Unless it is banned by governments from all over the world, i cannot see it falls from grace any time soon.
Yes, bitcoin will remain as a leader in crypto since it was very developed and it serves as a mother of other coins here. Because of its characteristic and usage makes it as a leader that other altcoins doesnt have. It will be replaced when something happen wrong to bitcoin and if it wont be solved. Also if there an altcoin that will boosts or maybe better than bitcoin. But for me its impossible to happen.