I've had this lilac for many years and this year there was a lot of dead wood and near dead wood. It's apparently a hybrid between Syringa meyeri ‘Palibin’ and Syringa pubescens subsp. Microphylla ‘Superba’. Can I do full renewal pruning on it, cutting all the old growth to near the ground? There is a lot of apparently healthy small growth; should I leave that?