I wish to point up that, old man zangetsu inside ichigo inner world, is a part of ichigo. If ichigo die, mean he will die as well. Juba form in ichigo, only trying to protect the host by sealing ichigo true power. Every plan is smooth at the first Until his plan got messed up by rukia, where she insert new source of shinigami power into ichigo and eventually make ichigo's sealed shinigami power to be awaken. Time by time, ichigo began to discovered more of his power during either training and battle.
Eventually ichigo noticed about the spirit in his inner world and get know the old man zangetsu and hollow ichigo. Upon connecting with ichigo, oldman zangetsu have to teach ichigo how to use his Zanpatou. He teach him, not because want him to be shinigami, but is to protect the host. If the host got killed, he will be die as well.....
However, oldman zangetsu, can't teach ichigo any Quincy move. Why? Because he do not wish ichigo, to know about he actually a Quincy power inside him. That's why he is using the hollow power to teach/help ichigo. And that's why the spirit who always help ichigo in battle is hollow.
Time goes by, oldman zangetsu himself have influence by ichigo resolve to become stronger stronger, and helped him in his path. And don't worry bro, oldman zangetsu is still inside ichigo, I think eventually he will teach ichigo about Quincy power. Just like what he did previously. Thats because, If ichigo die, he will die too.
DD