My buddleja is one of the dwarf ones and I thought it was dead last year. It eventually greened up a bit but it didn't bloom very well at all. Both Monty and Laura have said they cut theirs nearly to the ground and that they have success with it. I guess I'll give it a go, not much to lose with the condition it currently is in, but the one at Bonnie's cottage has been so nice and healthy and bloomed like crazy last summer. I'll pass on the caution, and suggest to her that we leave hers alone.
Lilacs, no problem here. They aren't ancient though - no thick trunks. The noid white one grew from a 4 inch passalong single stem which I got in 2014. It is finally about 5 or 6 feet and started blooming about 3 years ago. Trunks are still skinny. The noid purple one was one of the first shrubs I ever purchased for the garden back in 1994. It was in way too much shade, so although it stayed alive, it never grew very much and never bloomed. I should have relocated it years ago, but I never did. Then the oak trees that shaded it were some of the ones that have been dying over the last few years and were removed. That lilac has finally gotten the sun that it needs and has started to bloom!
I've seen Laura on Garden Answer deal with dying trunks on the ancient lilacs on her property, and boy these trunks are sizable. I never realized that lilacs could be more like trees than shrubs before I saw hers in some of the videos. She has removed the dead trunks, thinned and limbed up others. On some of them, she hopes it will give them additional life, but others she thinks they will probably need to be taken out sooner rather than later
