Hi,
I would say in this case if you are entering a private contract with the owner without the agent involvement, then you need not pay any commission but in this case, you have to come up with your own agreement. Also, within this renewal of lease agreement period, should there by any argument or problem arises, you have to try to settle the issue privately with the owner as the service of the agent had already been lapsed.
By engaging the agent in the renewal of your lease agreement, you actually sort of "insured" yourself against any possiblility of issues that might happen that could sour the owner-tenant relationship. Cos in this way the agent is responsible within the code of ethics of practice to service you throughout the contract period.
Hope my own point of view could be of help to you