回複：回複：回複：回複：回複：Questios for travel to China

Filing I-140 only doesn't allow applicants staying in US, only I-485 does. But due to visa backlog, there is no way you can file I-485 until your PD, which is your I-140 receipt date if it is approved, becomes current. Based on current progress, it may take 2-3 years when your PD becomes current, during which you must keep your non-immigrant status to stay in US. Since your I-140 was filed in Dec. last year, you are not qualified for H1b extension after 6 years.
If, only if, your I-140 is approved, I would suggest you go back to China and take Consulate process when your PD becomes current.