Myc can certainly die from antifungals, and some might never come back due to remaining traces and the fact that other organisms have colonized the substrate and produce their own antibiotics to keep competition at bay. Copper can have long lasting effects and inhibits all fungal growth to a certain extent.
Antifungals come in two forms: precise action meant for specific fungi - which are "broad spectrum" in the sense that they do a lot of collateral damage to fungi we haven't studied (either because they're hard to study, or because they're unknown, or because they're beneficial and don't require studying because they pose no economic risk).
The other form is broad spectrum - meant/designed to kill all fungi, no matter their shape or form by attacking mechanisms that are common in all fungi. Naturally with a bunch of collateral damage.
Some, if not all, antifungals affect bacteria, yeasts and archea too. Those are also important parts of the plants microbiome.
Plants can live in a perfect sterile environment if the right nutrients are provided, they don't always need myc. And over time, when antifungals break down the pots will recolonize fairly quickly, the composition and species variety will never be the same as in untreated soils though.
The key issue is that antifungal resistance can be passed on between different fungi. This is a process called horizontal gene transfer: instead of evolving in a tree-like pattern by making offspring, resistance genes can be transferred horizontally from branch to branch (on the evolutionary tree) in some cases. Instead of evolving in the traditional sense (generation passes on to the next), they just take genes from resistant organisms and incorporate those genes into their own DNA. This process is poorly understood in fungi, because they're a pretty unique type of organism by themselves. Prolonged exposure to antifungals can cause this to happen, sometimes with serious outcomes for us humans (resistant Candida outbreaks for instance). The process is reversible too; if genes aren't used enough, they can be shedded in a few generations because they become "dead weight".
Treating your plants for longer periods increases the chance of resistance to occur.
In pines and other conifers, we're dealing with long living myc. Fungi that can live for decades, if not longer. These don't shed genes easily and they don't evolve fast (although they can take up new spores and can form some kind of super organism with multiple nuclei from multiple parents). The plus side is that if they become resistant, the resistance will last for a long time. The downside is that this resistance can spread, and that it might take a very long time for resistance to occur in the first place. The competition is still the competition after millions of years, because they evolve as fast or faster than the good guys. It's an arms race with no end.
Personally, I try to stay away from antibiotics with the exception of lime sulphur for wood and copper sulphate for foliage applications. There are a multitude of first line options - peroxide, beneficial micro organisms, protective fungi, adaptations to the soil, or just removal of infected parts - and antibiotics are my final line of defense if all else fails. I have used them once in the past fifteen years of gardening.
Thus far, preventative measures have been enough. I have roughly 140 pines and I find +/- 40 needles with needle cast every season, I just pluck those needles off. Soil borne fungal issues are rare in my back yard and if they happen it's most likely because I created the conditions for them to happen.
I try to keep diversity high; every micro-organism produces its own antibiotics to fend off competitors, and this can help prevent much of our problems with no human interference.
I'm trying to "graft" myc too; use a wooden peg or a piece of cardboard, let it be colonized, transfer to the next pot. I also catch some runoff water from healthy trees and distribute it across the rest, since bacteria are more water bound. This however can bite me in the ass at a certain point; I could also be spreading disease. But that's a risk I'm willing to take.
I'm not against antibiotics, but I've seen in the lab what happens when resistance occurs. So I use them with caution, and when I do use them I make sure they leave no witnesses.
