I'm not sure of tolerances, but I've perused countless threads over several years on this forum about W124 head gasket failures that were more dramatic than yours and how heads had to be reconditioned afterwards.
None I read had issues with the head after repairs...and I'm sure mine will blow eventually.
I agree with Larry (as i usually do
). Until the head is pulled and inspected, I wouldn't consider it DOA just yet. The warpage that may have occurred depends on the duration that the head was exposed to the overheat condition...
..Save your money on the used motor...the head gasket repair and head reconditioning is already expensive enough!