1.How can Iran continue the war if U.S. & Israel pullback after missile & drone threat is over?
2. Missile & Drone attacks will eventually stop either because they run out or can't launch due to lack of infrastructure. How can launches happen when there is no electricity, communication, fuel or transport?
1. They still have proxies like Hezbollah, Iraqi Resistance and Houthis. And building drones and launching them doesn't require as much infrastructure as missiles, so they'll switch to suicide drones as the main force, perhaps new models with jet engines or turboprop around MACH 1 to make it faster than the usual Shaheds.
2. Infrastructure can be rebuilt. Unless the US is willing to bomb every single day or week to prevent the rebuilding of the infrastructure, you'd eventually need to put boots on the ground to capture territory to deny Iran's ability to produce and rebuild things.
3. And finally, no war can be won just from aerial bombings only on a country the size of Iran. The US intelligence just assumed that they have taken out most of Iran's missiles and launchers, but satelite surveillance and HUMINT can only go so far to find out the real scale of Iran's assets.
Not everything can be discovered just from satelite date as most of the action happens deep underground as Iran has 30+ missile cities and perhaps dozens more underground sites for all sorts of weapons production needs the US still don't know about.
I trust Iranian officials when they said they "prepared for a long war" because Iran is close to Russia and China so they would have gotten sound advice from them on hardening shelters, dispersal, etc , and those underground mountain bases are definitely secure from US bunker busters now, with means to get out from there via tunneling even if entrances are entombed by US bombings.