Thanks for any info people can share

The order isn't really religious in nature, given the fact that they managed to forget exactly what God they may or may not be following. So a monk might have any patron Deity at all.
My understanding is necromancy is unnatural and Monks of the Long Death don't like undeath...
So definitely Cyric, Myrkul, maybe Velsharoon, but not Kelemvor. Velsharoon might be a good possibility for use foo necromancy.The Long Death order worships the principle of death without caring much wihch diety currently owns the portfolio. They are more than willing to share death and its antecedent, pain, with others. Clerics of the previous god of death, Myrkul, chose to view them as part of their god's long-range plan. Kelemvor (the current god of the dead) veiws them as enemies, but is at least pleased that they do not actively promote undeath. Velsharoon (the god of necromancy) wants to woo them, but has not figured out how. Monks of the Long Death may multiclass freely as fighters, assassins, and blackguards. This order is quite strong in Thay, though not with the sanction or cooperation of the Red Wizards.