There are no negative info about consequences from people who failed SN on this forum, except two cases who got problems with kidneys.
But there is info from this Russian
article about SN poisoning consequences (first two paragraphs on page 6).
"In severe cases of intoxication due to degenerative changes in erythrocytes and a decrease in their resistance, hemolysis and secondary hemolytic anemia occur (on the 3-5th day after poisoning). In this case, hemoglobinuria, kidney damage (nephropathy with varying degrees of acute renal failure) and liver damage (toxic hepatopathy) can be observed. Severe acute vascular insufficiency (nitrite shock), coma, pulmonary edema may develop. The clinical picture of poisoning is highly variable. In some cases, changes in the respiratory organs come to the fore, in others - in the cardiovascular and central nervous systems, in others - in the blood system."
Also there are no comments about brain damage on this forum from people who failed SN.
But there are several articles which say that brain damage is possible.
From this
article (Page 2, Discussion, 2nd paragraph): "Nitrite is also a potent vasodilator and can
cause coronary ischemia and stroke as a result of hypotension, tachycardia, and hypoxia."
Also
article about survived case with brain damage: "Delayed post-hypoxic leukoencephalopathy (DPHL) is a demyelinating syndrome that occurs days to weeks after the brain has recovered from a coma. It is caused by the period of hypoxia and is characterized by mental disorders, extrapyramidal system symptoms, and motor changes. Common causes include cardiogenic shock, severe anemia, massive blood loss, and poisoning. There are only a few reports of DPHL due to nitrite poisoning in literature.
Most patients usually recover completely. However, DPHL can easily induce long-term neurological deficits. Within a few weeks, patients with mild symptoms gradually begin to recover some functions, such as speaking and walking. After 1–−2 years, most patients return to their baseline level, but following such poisoning, cognitive impairment including short-term memory deficits and fatigue may persist and hamper the patient's independence, reducing their quality of life."