Could conditional green card be a joint sponsor?

A person signs the I-864, not his status. Now if the CPR holder leaves the US and abandones his/her PR status, then it might be a tad difficult for the US government to enforce the I-864, but theoretically the I-864 remains intact.

what if the CGC holder file the I864 and then the CGC expires after 2 yrs, is the I864 still valid? in other word, the sponsor have to do the duty until the beneficier get the 40 points or becomes USC?
 
Top