They will both still be available. The 4770K will not just disappear. Pricing on the 4770K will remain the same, and the 4790K will also be around the same price.
^ This. Prices on high end Intel processors do not drop significantly until years after they are obsolete and it will be years before the i7 4770K is obsolete. Even the 2600K is still available for around $330 and it launched in January 2011. Going back further just look at the Core2Quad lineup for how well Intel processors hold value.