This is highly unlikely and it would be very expensive for an organization to uphold a 51% attack on Bitcoin. If an attack did occur, it could drop the value of Bitcoin. A solution to solidifying a P2P currency is to make the proof-of-work more difficult to corner. Even if developers release new protocols after an attack, there will be chaos as to which fork to trust and reputation could be shattered. The volatility of the value is another attack vector.