i864 问题

I am an American citizen in the process of filing the green card application for my husband, who is a Chinese citizen. But I am wondering: If we submit both together and get the I-130 approved, but the I-864 rejected, for how long would the approved I-130 be valid until? That is, how soon would we need to resubmit needed documents, etcetera, for I-864 if I-130 is already submitted and approved? Also, does this whole process have to start from the beginning if his US visa expires and then we apply for the green card from China instead? In regards to the I-864, I am particularly concerned about what USCIS might view as financially insufficient on my end, as the petitioner. Currently, my job would bring me yearly just a couple thousand under the threshold for poverty level. But, I have sufficient assets/funds that I have accumulated over several years, and they more than make up that difference (i.e., these funds are more than 4 times the difference between my yearly income and the minimum income level required). My concern is that USCIS will see that still as insufficient because the minimum aid is not coming from a running income, despite the sum of assets + income being more than enough altogether.