Since none of the keys are working as remotes, I'd have to agree that the problem is the wiring leading to the diversity antenna which is below the spoiler on the rear gate.
The last thread on this site (that I'm aware of) about this can be found
here
As you can see, that member tried to chase down a bad fuse - there wasn't one - and I think also checked the diversity antenna module itself (which isn't often the problem on these wagons). If you're reasonably handy and don't mind slicing into the rubber boot that routes the wiring, you can fix the wiring problem for pennies (well, for a couple of inexpensive splicing connectors, some electrical tape and cable ties to hold everything back together once you're done).
Here's what mine looks like once I got it all tied back together.
It's not beautiful, but actually better than what the dealer left me with when they did the first repair of this issue. They just wrapped the thing in electrical tape and called it a day. The tape quickly started to fall apart and come off. And yes, you can replace the whole gater/tube and it's inexpensive...but then you have to actually fully disconnect one end of the wiring harness at that location and that's likely a huge pain.