Janet Baraclough wrote:

Cordylines are not completely hardy. In mild areas of the UK they
can survive planted out in the garden, where they can grow much
taller than 3m .

snip

All agreed plus. When the frost does get at an established plant, all is not
lost. Simple cut down progressively from the top until you find non-mushy
trunk, then a little more. It will sprout happily and form a multi stem
plant.

pk