An un-named variety of buddleia was planted late spring '17, bloomed well, cut down this spring, bloomed well (and quite full foliage) and now 4x4. Residual Hurr Michael winds uprooted it. Staked and watered, but now uprooted again. When uprighted this time, the root ball could not be compressed back to ground level. It would be possible to dig around it to resettle the rootball if i cut it back, which would also stabilize it vs. future winds. Am concerned that if frost is late, there could be new growth that is zapped, and don't know if would cause residual damage. However, since will cut back anyway in spring, and frost will probably come soon, it seems best to cut back now to about 2' which will avoid further wind movement, and allow resettling the roots to proper soil level. Then in spring cut back as usual. Do you suggest a different strategy?
Yes, we'd think that getting those roots well-settled before winter sets in and the ground freezes would be your priority. Roots will continue to grow even after frosts, until the ground freezes solid.
Some of the newer Buddleia seem not to be as winter hardy as others.
That said, in colder areas north of us people often expect their (older variety) plants to be killed back to the roots each year and start anew in the spring.
Butterfly bush is on the invasive plant radar as they can seed themselves into wild areas, replacing native flora. Be sure to pull any 'volunteers' you find in your yard.