As far as I know actual sales of US "Forever" stamps (as opposed to overall number of stamps printed) is data that is hard to come by.
Therefore, I found it rather interesting to note that the concluding line of this news release published 09/24/2012 suggests that of the 40 million Celebrate Scouting Stamps issued on June 9, 2012, 9.8 million have been sold as of August 31, 2012, which comes out to less than 25% (specifically 24.5%) of the overall print run in just under three months time.
https://liteblue.usps.gov/news/link...news25s2.htmEven if the sale of these stamps were to continue at the rate of 1 million per month it would take another 2-1/2 years at that rate for the overall quantity of stamps printed to be depleted.
Based on this information, it would be my guess that when these stamps are taken off sale, a sizable quantity of them will remain and probably be destroyed.
It seems as though this is yet another example of excessive printing of stamps that are seeing much lower use than in previous years.