Merged mining does not replace the seal. Every Kronex block is sealed by
kHeavyHash. Merge-mining proofs ride inside the block and
earn rewards; they do not decide which block is valid.
The parent chains
Dogecoin rides along on the Litecoin side, on the same Scrypt work.
Each chain carries its own difficulty state and its own reward curve, so
SHA256d and Equihash work can be priced differently while both stay accepted.
Losing one parent chain reduces the work flowing into Kronex; it does not stop
the chain, which is still sealed by kHeavyHash.
How the binding works
A merge-mining payload reduces to a single field in the Kronex header,KRNXAuxRoot, and that field is part of the proof-of-work pre-image — not just
of the block hash.
That distinction is the whole security argument. The payload decides who gets
paid. Anything covered by the block hash but not by the pre-image could be
rewritten after mining without invalidating the seal. Binding the root into the
pre-image makes rewriting it cost a re-mine.
Blocks with no payload keep the stock pre-image. Stripping a payload zeroes the
root, which drops the field entirely and changes the hash just as much, so
removing one buys an attacker nothing either.