That will definitely change the supply and pricing level of Bitcoins, but if the technical aspects are not figured out by 2020 then I think Bitcoin will have much bigger issues than that. Less coins available for miners doesn't automatically mean less profits, because if the pricing level increases it could have no influence over the miners profits.
Miners are already making relatively slim profit margins as it is which allows for only the most efficient and biggest miners to run their hardware at a profit. The market will adjust accordingly with the halving of coins, meaning only the most efficient mining operations are able to stay profitable.