Hezbollah, of course, is Iran's client. Lately Iran has been outsourcing Hezbollah terror leaders not only to fight in Syria but also to train and lead Shiite forces in Iraq and Yemen. As Foreign Affairs noted recently,
Hezbollah’s involvement in the war in Syria may have originally focused on supporting the Assad regime, but it now considers that war an existential battle for the future of the region, and for Hezbollah’s place in it. As a result, the group’s regional focus will likely continue for the foreseeable future. Together with other Iranian-backed militias, Hezbollah will continue to head an emerging Shiite foreign legion working both to defend Shiite communities and to expand Iranian influence across the region.However, Hezbollah's base in Lebanon is weakening as it is expanding its footprint across the Middle East. Hundreds of Hezbollah fighters are reportedly refusing to go to battle. Lebanese media are uniformly critical of Hezbollah's adventurism in Syria and holding the government hostage.
If Nasrallah was assassinated now, it could deal a major blow not only to Hezbollah but to Iran.
Such an event would embolden rival Lebanese parties to push Hezbollah out of the way. Iran would not dare to directly interfere militarily in Lebanon as countries debate the Iran nuclear deal. Iran is now dependent on Hezbollah for outsourcing its influence across the region (as well as terror) but without a leader Hezbollah's influence in Yemen, Iraq and Syria would be blunted and perhaps eliminated - dealing a great blow to Iran's regional aspirations. Without its Lebanese base, Hezbollah would have no anchor and would lose a great deal of influence.
On the other hand, if (and when) the world acquiesces to the Iranian nuclear deal, Iran would be emboldened to increase its aid to Hezbollah and increase its influence, an influence that within a short time will include nuclear bullying.
This is the perfect time for an espionage agency to pull out the stops and find the basement Nasrallah is hiding in.