this has been a really common question this year. how dead it is will be sorted in a matter of time. chances are it is dead though.

Something about your description suggests to me that you might be speaking about a Phormium rather than a Cordyline, so please google to make sure. Cordyline usually has a woody stem or trunk, Phormium doesn't. If its Phormium, you can remove or cut off all dead and dying leaves at the end of this month (unless its freezing cold). If its Cordyline, check the trunk for signs of rotting - if there is rotting, depending on how bad it is, you will have to cut back past that point, but this is best left till April if possible. Then just wait to see if it puts out any new growth - you may have to wait till June to be sure, and if it does grow either up the trunk or from the base, cut back to the new growth.