You cannot convert lawful permanent residence to a 10-uear B-2 visa. Your parents need to apply for a re-entry permit. This is the best way to prepservce residence, but as you noted it is not a guarantee they will not be deemed to have abandoned their residence. Your parents would likely face difficulty obtaining B-2 visas in the futre if they abandon their residence unless they can establish very strong ties to China.
Answered on May 27th, 2016 at 2:13 PM