It's worth a go. They'll often throw out new shoots from the trunk or even the base after the top has been damaged. They've got to replace their root system, too, after the transplant, and that can be quite extensive.

If you can give them garden room until the first year's up, at least, then they'll have a chance to come right though they obviously won't have the common single stem - they'll have character much earlier.

Righto. Thanks for that. I planted them the day after they were delivered. They still had good rootballs, and I've come across healthy looking roots when weeding near to the base of the trunk, so I think the roots are ok.
Our next-door neighbour had a 5foot cordyline which he chopped the top off, and then dug up the base, chopping most of the roots in the process. He just dumped it over his back fence. I found it a few days later, and planted both the truncated stem, and the lopped-off top. As with the big ones, all the leaves dropped off, but after several months, tiny shoots came out of the trunks, on both halves, and there are now two thriving and vigorous plants.
So, I'm hoping their bigger cousins will show equal powers of regeneration, and re-sprout sometime this autumn, hopefull not right at the base though - it would be a shame for a 15 foot high trunk to go to waste! Or indeed five of them!