Assumedly the agreement you signed gives you the right to terminate the agreement at any time. Terminate it. Look, people get busy and they often are too optimistic about how much energy they can put into things or they could simply be embarrassed about lack of progress. Call the advisor and see if they get back to you. Then just let them know that it really hasn't worked out and you think the best course of action for both parties it to terminate the agreement.
Their response could be:
* "Yes, I agree" ... then done.
* "Hey, I know I haven't been too helpful but I've got more time and I'll get on it" ... if you believe them, your response can then be: fine, but I'd like to push the cliff date back 3 months. they'll almost certainly agree.
* "What? Hey, I helped you do X and Y. OK, I haven't done Z but now you're just trying to screw me." ... I imagine this is the scenario you're worried about. At this point you just need to make a principle vs. practical trade-off based on how strongly you feel and how strongly they feel and the probability that they'll hurt your chances of success. Also think about the message it sends to the rest of your team - is it likely to bring you together by not putting up with poor performance?