A heart transplant is done only if the pumping efficiency of your heart is reduced to a level where you cannot survive for lung without a transplant. (Ejection fraction
Depending on the anatomy of the blocked grafts and the native coronary anatomy, it may be possible to do angioplasty/stenting to some of the blocks to relieve the ischemia
. Sometimes, a redo CABG may be possible if conduits are availabe (veins/arteries which can be used to bypass the blockages).
There are also medicines which can be optimized to improve your cardiac function