Whether they can "hold on" is more of a sociological and cultural question than an economic problem as it stands.
As during the Iran-Iraq war, they went into it from a much worse starting position and persevered until the very end.
And this time, the US sure did damn
everything it could to unite the population behind the regime due to extraordinary incompetence.
Undoubtedly, this situation has already created unprecedented national unity even among the regime's previous haters and
hardened it.
Since they have basic self-sufficiency in crucial things (and friendly help), I think that if it comes to it, they will outlast the US.
Instead of uniting, this war is rapidly polarizing the already pretty polarized and angry US population.
Support behind the president and his war effort from the onset was meager, and it could only get worse.
Moreover, judging from CSIS reports, the US has already spent half of the previously used missiles & interceptors.
If the US chooses to resume this war, it will have to involve a higher rate of casualties and possible ground operations.
Which actually plays into the Iranian hand the most. Moreover, the US economy is unhealthy as it could be.
The US is not going into this war from the position of WW2, but from the biggest leveraged scam economy in history.