My mother had cabg surgery but the surgeon was unable to bypass left circumflex lcx artery 90% block. rest 2 were bypassed. what is the risk for lcx?

Depends: It depends on the particular anatomy of the branches from that part of the left coronary artery to the back of the heart. Small blood vessel branches will not keep bypass grafts open because the flow through them is insufficient. Collateral (feeding) branches from other adjacent arteries may feed that area. In some cases, angioplasty (ballooning) with stents could be considered.