Yes. That would definitely be a bad thing [no math classs senior year] .
All depends on. Basic evaluation is made with first 6 semester transcript and depends when the file gets reviewed, the 7th semester transcript might not even be considered. If a candidate's standardized math score is high and he or she took some sort of Cal class junior, I think not taking a math class senior year will have minimum impact on the admissions decision.
Of course, it will probably hurt during the first year math at West Point.