I am sorry for your loss.
I don't practice in Minnesota so I am speaking from general custody considerations rather than a specific knowledge of MN law.
Since the child wants to stay with you and the father has not maintained any contact for ten years, you might be able to obtain custody or guardianship over his objection. It might be possible for an attorney to negotiate a resolution with him rather than just filing an adversarial guardianship case without advance discussions.
If the father's absence was his choice rather than your deceased partner's and there are other deficiencies in his parenting abilities, the ability of a de facto or psychological parent without any legal safeguards to overcome a birth parent's claim of rights might be more likely.
I would suggest that you use a lawyer referral service rather than a question and answer forum to try to find an experienced family law attorney in your area who is knowledgeable about and interested in LBGT parenting and partnering issues. You might want to contact the National Center for Lesbian Rights (NCLR) which has family recognition and custody issues listed amongst its issue areas of concern. There are also Parents and Friends of Lesbians and Gays (PFLAG) chapters near you. They might be able to point you in the direction of a knowledgeable attorney.