Can a MEB be denied if SM denies surgery for reasons listed below?

I refused surgery when I broke my ankle on active duty, as I felt if surgery was neccesary I would want to get it at a hospital of my choosing and not on base with some intern doing it. They still approved a medical discharge at 20% disability, though because I turned down surgery I was probably denied a higher %.

Your best source is JAG. MEBs require a determination of whether the refusal of medical treatment was reasonable.
I doubt UCMJ for refusing surgery, but you may find that the condition will not be rated by the MEB (Army).
VA compensation likely wouldn't be denied due to refusal of surgery.
References.
AR 635-40, Appendix B. c. Failure to comply with prescribed treatment.
(1) There are many conditions, such as... certain injuries, which may be improved sufficiently by treatment to prevent disability, or to significantly decrease it. If a Soldier unreasonably fails or refuses to submit to medical or surgical treatment or therapy, or take prescribed medications, or to observe prescribed restrictions on .... activities, that portion of the disability that results from such failure or refusal will not be rated where it is clearly demonstrated that—
(a) The Soldier was advised clearly and understandably of the medically proper course of treatment, therapy, medication or restriction.
(b) The Soldier’s failure or refusal was willful or negligent and not the result of mental disease or a physical inability to comply.
(2) Notwithstanding the above guidance, MTF’s should not forward MEB’s involving refusal to submit to medical care unless a determination has been made by Office of the Surgeon General that the Soldier’s refusal was reasonable according to the procedures set forth in AR 600–20, paragraph 5–4c. PEB’s may return cases to MTF’s for compliance with AR 600–20.
5-4. 5. e. c. (2) Generally, refusal of medical care is considered unreasonable without substantial evidence that the treatment is inadvisable. However, in deciding whether refusal of medical treatment, including surgery, is reasonable or unreasona-
ble, the board should consider among other things—
(a) Existing evidence that the physical or mental treatment is inadvisable.
(b) Previous unsuccessful operations and procedures.
(c) Any special risks involved in the proposed medical treatment.
5-4. 5. e. ....Copies of the medical board proceedings are provided. If the Special Court-Martial Convening
Authority orders the Soldier to submit to treatment and the Soldier refuses to obey, the commander may take—
(a) Disciplinary action according to MCM.
(b) Administrative action to separate the Soldier from service through retirement, discharge, or other legal means.

Yes you can be denied. You cannot expect the military to separate you with monitary ramifications if you can perform in another MOS. While you are serving it is not your option whether you do or do not serve in another MOS. If you refuse to change MOS you are simply going to be discharged at the time of your ETS or possibly chaptered. All of this is hypothetical, but remember you volunteered to protect your country, if you cannot serve in one capacity you can serve in another. If you choose not to, what makes you think that they owe you something, particularly since you are refusing to be repaired. Thank you for your service.