Are Annexin V binding to phosphatidylserine (PS) reversible?  

Yes,  Annexin V binding to PS occurs only in dying cells, is calcium dependent, and reversible. Each Annexin V molecule binds approximately 50 exposed PS monomers. However, the initial events may be reversible, but in turn, initiate irreversible processes belonging to the “execution phase,” such as externalization of phosphatidylserine in the plasma membrane and fragmentation of nuclear DNA

http://cancerres.aacrjournals.org/content/60/16/4623