The behaviour of PCA9544 is according to I2C protocol scheme. A device that doesn't utilize clock stretching or busy state signaling will behave completely predictable, multiple devices with same address won't interfer, just take the same data.
But...
- why don't you use hardware addressing?
- operating two series connected MUX devices with the same address results in many unavailable MUX combinations. Only the first level can use all pathes. So it seems pretty useless.