I believe there will be two chains, one with new protocol and major network power and the other with the old protocol and very limited network hashing power.
So I believe the old chain will be neglected and the price will fall just because of transaction issues and the new chain will get more attention because of faster transaction times and the price of it will increase.
The beauty here is that when network split, you will have coins on each network. Even if the price goes down 50% on one chain and the price on another chain remain, I think you can see the scenario here, you profit 50% from the chain split. But the price would be unknown since the event is yet to happen. If the chain is bound to split then it would be the best time to buy Bitcoin since you can have bitcoin on either chain, thus profit is expected.