No they won't, this is what's known as reversion, where a variegated plant suddenly produces all green growth instead. Cut out the branches with the plain green growth on.

Yes, cut the green shoots out or they will take over the whole plant. They have more chlorophyll and so are stronger than the variegated shoots. My Pieris does this too. I also noticed that only one shoot had flowers on and, yes, you've guessed! It was on the plain green shoot!!

Thank you both very much for information, we are very grateful, and will follow your advice rightaway.

I looked in our gardening books, of which some are very large works, but I could not find any information regarding this topic, so we are very glad we asked the question.