I would cut the plant back cleanly to about six inch stumps. It will regrow from the bottom, bigger and better than ever.

Leaves would also sprout from the old growth (or rather, it may continue growing taller and making new branches). However, I have also heard that some owners cut their oleander down to the ground anyway, and it returns just fine.

I lost three that I had out for over a year and two that were in pots. Three larger ones were not hurt. I have been growing oleanders for 20 yrs. and have never had any trouble with them until this winter. I was told that I could not expect them to survive cold weather where I live. They are easy to root and and I will root several this spring.