Hi!
I am one of those who do not kill nobles and instead try to meet demands. However, I have to admit that I have had too little playing time in 39+ versions to get the full impact of current nobles.
I actually had one annoying incident when a freshly elected mayor (replacing another living dwarf at the top of the hierarchy) figured he should celebrate his election by making a mandate for adamantine items ... right, in a fortress in its second year without smelter, smithie, HFS, magma, chasm, cave, cave river or any other notable feature and maybe just three excavated z-levels.
Because of the high replacement rate of versions, the fortress has been scrapped before long, but if I had kept it, in that particular case, I would have tried to replace him democratically (since it was a mayor, that was an option, fortunately): Set him to do all labors and at the same time give a dwarf who is not an adamantine addict plenty of free time to bolster up social skills and make friends among the voters.
Of course, that trick wouldn't do for any of the real nobles, but I think it is more interesting to live with the risk and try to keep them well-fed and happy rather than murder them until the RNG gets tired of it and appeases you.
Deathworks
BTW, if you melt down metal goods, eventually you will get a bar of that metal in the smelter. Would that bar also count for mandates?