HI Dave, I'd say get the D7000 now. It has the capability to produce outstanding photos whether a newer model comes out or not. It's a safe bet, plus your probability of successful photography will increase if you have more time to practice.
Once you're back and a new model comes out, you could sell the two D90's and get the newer model DX. Then you'll have a D7000 and a new DXXX.
Regarding the D7000 being discontinued, The D90 hasn't even been discontinued yet, so why would Nikon discontinue the D7000, which is newer technology and a more successful product? Anything is possible I guess.
Have a great time on your trip and post some photos.
"Red is gray and yellow white, but we decide which is right ....and which is an illusion"