Do you see a difference in these statements that I have underlined in the study by Morgan and Scazo in their paper "Improved Shock Absorbing Liner for Helmets"? What they actually said is that once the cracks occur, further ability to absorb shock is compromised. But tables (which I'll copy and post when I get home) in the appendices of this paper show conclusively that even with severe cracks, many of the foams (with one exception) compress and absorb a lot of shock.
Firstly. Morgan & S is NOT my source for the "if the liner fails the helmet" fails.
Secondly, the table doesn't say what you think. All of the helmets were tested AT BELOW the helmet threshold velocity. The table says "If you're wearing a helmet in a low speed accident it may still crack; this cracking may be internal - ie when the foam is collapsed and the force hasn't been fully absorbed the helmet will then be smashed develop a few crack lines"
This is not the same as "If a helmet hits AT ABOVE the threshold velocity and the liner FLIES APART the foam will work anyway".
And even if you are unqualified, simple common sense and goodwill should have told you this - all you had to do was to check the drop distances quoted in the table and convert them into velocities, which is 12 year old physics. (Hint - your head is already at 1.2-1.5m above the ground when you're not moving on a bike! How much speed is needed to add the velocity of another 30cm of drop?) Really - either you don't understand the fundamentals here, or you're being deliberately deceptive. Your method of argument seems to consist simply of hitting facts with a hammer to force them through un-fact shaped holes; if the facts get warped beyond recognition in the process you don't seem to care.