Pyrocanthus Roots?

Mine, espaliered on an old stone wall, was about
15 years old and had extensive roots, but I truly believe that it depends upon the soil and growing conditions for the most part, light playing a big part of it's health above and below the surface of the soil.
If given a lot of fertilizer and a large plant over 6 feet wide/and tall, it's likely to have deeper roots. If smaller, the root system might not have fully developed. This has been our experience. We made
the mistake of taking too many mature plants out from around a foundation once when we should have learned how to enhance the older plants we had by
appropriate shaping and what each plant perferred, going WITH the plants rather than against the plants. It almost killed my poor husband back then

because we'd never attempted to get roots out before that time.

We regretted it forever. I've seen a lot of sparser less mature plants successfully uprooted and replaced with nice newer more attractive ones during remodeling and refurbishings. This became a hobby of mine, learning more from trial and error over the many years and thousands of plants planted.

However, I cannot emphasize too strongly how important it is to learn about any plant AND the soil in which you plan to plant it in, as to drainage, properties, chemicals used previously, sun exposure,
how winter cold will affect the plant(s), watering needs, etc. It isn't so easy without a lot of homework to help a plant survive. Also, if the old
plant roots are left in the ground, it may return all
snarly, or come up where you least expect it.

I disliked the Pyracantha more than any plant I ever raised because the pricks are so burning, thus it's name. The berries are attractive, but the thorns are just not worth it to me. I worked like a Trojan to keep my espalier finely shaped into a wonderful pattern but had so much Blight with that plant I could

not keep it looking good. I finally just cut it down in
frustration, not worrying about the roots, I believe, now that I think back. Few residents in this city have them anymore for the same reasons, but the Blight just might not be a problem in your area? Good luck.
God bless you. : )