Not necessarily. 7nm would work fine in place of the 2nd chiplet. If they add a cache for the graphics chip, it would help with the small latency penalty that exists. Chiplet to chiplet latency isn’t terrible to begin with, and is much lower than PCIE latency.With the setup AMD has right now, the IGP needs to be on the same die as the memory controller. So they could make a new IO die on TSMC 7 nm and use that. I agree that they are more likely to do monolithic.
I still think there's a chance they put a GDDR6 controller, although obviously that would only be on mobile.