Roots of many garden vegetables penetrate 8 to 12 feet deep. I suppose that the fungi are growing right along with the roots. So if I till super deep, say 6", then that's still only 4% of the soil volume that the fungi and roots are using. And if I do routine cultivation of weeds, at 1" deep, then that's disturbing less than 1% of the space used by the roots/fungi.
And it seems to me from watching them grow, that fungi are self-grafting, and self-regenerating. Any part of the fungi can re-grow itself and can graft itself to any of it's kin with which it is compatible.
Roots do go down deep, but the vast majority of biological activity in all soil is in the top few inches, what a soil scientist would call the A horizon. The limiting factor for deeper activity is Oxygen availability. As far as I know, every known mycorrhizae species found so far is aerobic.