How is Dark Messiah connected to Heroes of Might and Magic?

The backstory for DoMM will be the "Tribes of the East" expansion for HoMM5. One of the key characters in the expansion will be Arantir, a Necromancer who opposed Sareth (the Dark Messiah) in DoMM. Thus, DoMM is the concluding chapter of the HoMM5 storyline. Nival and Ubisoft will undoubtedly choose the canonical ending, in which Sareth does not liberate Kha-Beleth.