Curious about purchase

83 RX-7 Gsl, 2000 Mazda Protege LX, 2011 Mazda3 Sport i
My buddy bought a ms6 a while ago and suddenly the key stopped working so he brought it to mazda where they told him they couldnt fix it for him. I was curious if anyone has any idea what the key fob actually communicates with or if this would even be worth asking to buy for myself?