Even with 64 blood clones, the pain of division, the life force cost of division, and the loss of life force to maintain the state were significant. But it was worth it because he could maintain it indefinitely, and his escape potential had been maximized.
64 blood clones meant that each one possessed 1.56% of his life force. The loss of one of them wouldn't be felt much.
Apart from the pain he would experience from the destruction of his blood clones, their elimination would actually improve his control of the rest and increase his chances of making them escape.
As long as one of the 64 can escape. That one will be able to turn back into his true form and survive. Of course, if only one escapes, that will mean he had sacrificed 98.44% of his life force for the chance of survival.
It is a worthy exchange for survival in his books. It is just too close for comfort.