According to a post by user wt1 on stampcommunity.org from 2013 (in reply to another user who had picked-up a book of Minuteman and similar stamps at an outdoor antique market), they should still be redeemable at face-value:
[...] as technically they still have "face value" upon application to:
US Bureau of the Public Debt
200 Third Street
Parkersburg, VA 26106-1328
They can be redeemed for cash or used to the extent of their value in partial payment for a US Savings Bond.
Although it also notes that they are probably (depending on condition) worth more philatelically.
As the link you gave states, the intention was that these stamps would be used to buy Series E War Bonds, where a full book of 75 x 25-cent stamps (face-value $18.75) could buy one $25 Series E bond which would mature 10 years later.
The Wikipedia page on the Series E bond notes:
After the war, Series E Bonds continued to be sold until June 1980 as part of the United States Savings Bonds program, thereafter being replaced by Series EE bonds.
and the Investopedia page on the same subject also notes:
The exchange of E Series bonds for H Series [was] allowed until 2004. That exchange is no longer offered. Instead, holders of mature Series E bonds can redeem them at financial institutions such as banks at an accrual value determined by the U.S. Treasury on a semi-annual basis. The final round of Series E Bonds stopped earning interest in 2010.