AC-coupled RF Microstrip routing over power plane
This isn't a push-pull driver like the ones in the paper, it's a Class C amplifier (some of the others are Class A).

This has nothing to do with the microstrip structure. It's a whole separate issue that you should deal with separately.

MMICs have a nice big flat low-inductance ground connection through their thermal pad, but typically only a few pins for power. I can only assume any microstrip on-die will be referenced to that ground plane, which I'd imagine would create a discontinuity when transitioning to the PCB microstrip.
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Eventually this all runs into a coaxial connector whose shield is connected to ground. Unless I connected shield to power (which seems like a terrible idea), wouldn't that create a pretty significant discontinuity as well?

Both of these are essentially the same issue. They both mean that your return path will have to find a route between the power plane and the ground plane. You will want to place a bypass capacitor near where these discontinuities occur, giving the return currents a path between the coaxial and on-chip references and the microstrip reference plane. At 433 MHz, this shouldn't create too much trouble if the capacitors are chosen well and not located too far from the discontinuities.