I think he should ignore President Obama and send the ultimatum. But he must be prepared to follow through with his threat. The truth is Israel does not want sole responsibility for the West Bank. The financial cost would be tremendous as it would all fall on their shoulders as the occupier.
Russia: U.S. plan to provide air cover for Syrian rebels undermines Damascus fight on ISIS (Reuters)
from the article: In rebuff to Obama, Abbas says he will send ultimatum to Israel