I don't think Iran can sustain war for 6 months.
See, it's not about missiles and ammunitions but economy.
Iran was already under sanctions. It can't even supply oil to keep something going anymore due to war. There will be shortage of resources and funds to keep going.
Russia already has hands full due to Ukraine and China won't poke it's nose too much either as long as it gets oil anyhow.
Iran hardly has any other allies that can help it to sustain this war economically.
So, I don't see how Iran can sustain war for 6 months. It's economy was not really that strong to begin with and now it would be under immense pressure as well.
6 months doesn't make sense .
To me, it appears like they are preparing for the worst case scenario but I don't think Iran can last more than a month or may be 2 against continuous barrage of missiles, rising casualties, economic isolation, limited funds and not even having allies to support it economically.
Another factor is - Strait of Hormuz and fuel supply.
Fuel costs are rising and supplies from Gulf and Iran are taking heavy hits which will affect entire world economically.
Countries don't have enough fuel reserves. And, with Strait of Hormuz being in a war sensitive zone, even supply from other regions would be affected.
There would be increasing pressure globally to end the war as day goes by.
I don't see this war lasting more than a month or two