given that there are many many thousands of prints over 100 years old in great condition and not toned in selenium or gold I wonder why people get so hung up on archival permanence. Fact is the most likely causes of your prints going bad are the environmental conditions they are kept in providing you have applied good processing with proper wash. Partial toning will make them last for probably over 200 years if someone keeps them in constant humidity, constant temp and low lighting. But fact is people won't keep them in those conditions. They are likely to hang them on a wall above a radiator/heat source or somewhere in the house with wild swings in humidity and temperature which will vastly reduce their life. You are just making life difficult for yourself for no good reason by trying to tone to completion for permanence sake.
Gursky c-print sold for 4 million euros. It will probably only last for 20 years before significant deterioration. What have you got to worry about?
20 years for a c-print ? you are very optimistic...