I personally do not think a ground invasion of Iran is on the agenda. At least not any time soon. Maybe a few years later, if the regime does not get their shit together.
I think the worst case scenario, and possibly the most likely scenario, is that they will attack Iranian nuclear sites with limited success and call it a day, exaggerate it in the media to make it look like the problem has been resolved.
They will destroy uranium mining infrastructure, centrifuge assembly and supply chains, all tunnels and routes to underground facilities. They will destroy some accessible parts of Natanz with success.
However, I think the main chambers of enrichment at both Natanz and Fordow will survive the attacks.
If Iran decides to respond to these attacks, they will then go for our critical energy infrastructure like oil and gas terminals, power plants, etc.
I highly doubt it would ever get to the point of a ground invasion, which is highly costly and completely unpredictable. The US may very well lose this war in that scenario. The US can easily win a series of aerial campaigns against our nuclear sites, but is likely to lose a ground invasion of Iran with trillions of dollars wasted.
However, I don't see why Turkey or Pakistan has any interests in defending Iran whatsoever.