One imagines that Virizion, of all creatures, would be the very last pokemon to accept mechanization; it protects the forest from the factory, not the other way around. Iron Leaves is the ultimate Paradox Pokemon – a testament to a future arms race which will someday give organic life's most passionate defenders no choice but to mechanize themselves in order to hold their own in battle.
We can not know what becomes of nature in the so-called "iron future", but the failure of the Violet Book to record a single fully organic pokemon can only have extremely negative implications. Keldeo's absence may add a further touch of personal tragedy to Iron Leaves' experience, but however popular it may be in science fiction, this notion can only be regarded as speculative; the Violet Book's purpose was not to give an exhaustive survey of the future's pokemon, but to record those species the author or authors personally encountered before returning to our own time.
For what it's worth, Iron Leaves is described therein as peacefully grazing; whether 'grazing' in this context is proof that organic grass survives, and whether this paradox pokemon was acting like a typical herbivore or simply too depressed to do anything else, is impossible to say. It is worth noting that there was nothing in the area where it was sighted which Iron Leaves had any need to protect, and also worth noting that every known attack comparable to the psychic blades on Iron Leaves' horn and neck, which appear to be the creature's main weapons, requires strong willpower to use effectively.
If one wishes, despite all the evidence, to have hope for the far future, then one should remember that legendary grass pokemon harbor within them the power to create nature anew.