If you create something without using any natural resources, then you shouldn't have to pay any taxes on it — it all belongs to you. Well done! If a large company does it then same — it's good to use less resources, and taxing their use encourages people to use less. But you will still probably want to live somewhere (and eat food grown somewhere, and drink water that fell somewhere), and you pay tax on what you use, instead of the income you generate.
Georgism is about taxing resource consumption, not income.
If the employer leaves, the town will be unable to sustain itself, everyone will leave, and the land will return to the wild.
Given this setup, under Georgism, what is the amount of property tax the major employer should pay? The correct amount of tax would appear to be negative.
https://www.gameofrent.com/content/is-land-a-big-deal
and the vast majority of that real estate's value is in land
Is that true? Most of the value derives from the location - if you doubled the floor space over the land, the value of the land+improvements would double. The land isn't contributing value.