Q.saving indoor yucca
I recently planted my indoor yucca of 15 years outside in a north facing garden. Oh dear! The leaves have turned a very light green and continue to fall off on a daily basis. It has been subject to a few very cold/frosty nights – maybe a little premature to plant out. It’s well over 6′ tall at its highest point with 3 stems (the other 2 being shorter). How can I rescue it? Please help. It’s my pride and joy from a baby! Thank you.

You are correct in that perhaps it was a little early to move your plant outdoors. Yucca should not be transplanted outdoors until the weather is consistently 50+ degrees and the ground has begun to warm. In addition, the plant may be going through a bit of shock since it was accustomed to indoor life for 15 years. Your pride and joy is probably stressed out a little.
I am going to recommend that you review the following articles. These articles will give you ideas on how to pamper your baby back into good health!
Frost damage on yuccca plants:
https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-cold-weather.htm
Transplant shock:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm
Care of outdoor yuccas:
https://www.gardeningknowhow.com/ornamental/foliage/yucca/caring-for-and-landscaping-with-yuccas-outdoors.htm