Very valid concerns! AMD's current die-to-die interconnects have some pretty abysmal energy/bit. Really hope they can pull off something similar to Intel's EMIB maybe?
The rumors saying Strix Halo will be a multi-chip product are saying it's re-using the existing Zen5 CPU chiplets from the desktop and server parts and just replacing the IO die with one that has a vastly larger iGPU and double the DRAM controllers. So they might be able to save a bit of power with more advanced packaging that puts the chiplets right next to each other, but it'll still be the same IF links that are power-hungry on the desktop parts.