I recollect that British Airways has previously contacted Executive Members with an offer to buy tier points to help them requalify for Silver Membership in the last couple of months before the end of their membership year, but this may have been a one off. Last year, British Airways allowed Executive Members who had not earned sufficient tier points to continue as a Silver (or Gold) member on the basis that cabin crew strike action may have led to passengers switching to other airlines. So, there has been some flexibility available to Executive Club members.
Even as a Blue Executive Club member, the passenger could continue to receive the benefits of fast track bag drop, security, and boarding, and lounge access, by travelling in Club Europe, Club World or First.
Perhaps this posting on FT will encourage BA to change its mind though!