I had a similar one that was about 2' across... I lopped off the top, remounted it, and sold it - someone out there is looking for that kind of centerpiece. The base will regrow a nice crown in a matter of months. In fact, I have now lopped off 3 complete crowns from this
toadstool. If you just cut the top off, you don't lose any diameter. Little toadstools are a dime a dozen... but a big one can be worth a lot more.
Anyway, it should be fine however you decide to frag it. They're quite hardy.
Good luck,
Danielle