I suspect the real problem for Ukraine isn't whether or not Russians learn how to reduce the effectiveness of HIMARS, but whether or not NATO (primarily the USA) can replenish weapons systems and materiel at the rate needed to keep Russian invaders on the defensive. As NATO countries run down their far-too-tiny stocks, and as Ukraine wears out and exhausts its weapons systems, Russia can - despite all the evident incapacity of its forces - regain significant advantage simply by enduring and throwing ever-more bodies at the problem. Putin's very survival depends on achieving "victory" whereas in the West we're flabby, spineless, self-indulgent, and lack any capacity for sustained effort on behalf of third parties.