In Nevada, if the Mother dies is her adult children still considered to be step children of her husband?

Youir question is really one more of etiquette than law.  The laws relating to custody and support that are potentially applicable in a step-parent relationship end at emancipation.  For details about wills, trusts, and estate, you should consult a specialist in that area, but the rules of intestate succession probably do not include step-children, either.  So from the legal perspective, the question would be "treat them in what way?" and "considered" by whom?  If you asked the question of Dear Abby, the answer you would probably get is that most people can use all the love and support they can get, so if you wish to remain close to your adult step-children, feel free to remain so.