They're supposed to be enemies the last couple of years, although US is pressing them to be friends again due to the the regional tensions and many meetings for reconciliation have taken place and some analysts consider them successful. Greece/Cyprus/Israel have signed a strategic and energy alliance. No idea if the alliances will change if SHTF, the only thing i know is that Israeli officials have stated that they prefer Turkey more than Greece as an ally because of her geographic position in the ME and Caucasus, but the average Israeli person prefers the friendship with Greece than Turkey.