If it were me (having grown it from seed and looked after it for 20 odd years), I'd most definitely give it a further year in the ground, before making a final decision on removing it (fingers-crossed it won't come to that).
In the meantime I would:
- Spread a 50mm layer of good quality compost all the way around it (about 1 to 1.5m diameter). This will feed the shrub naturally and slowly.
- Keep a regular eye on it & check for any sign of pest damage/infection.
- In warm, dry spells, make sure it gets a good drink (water slowly & deeply).
- Propagate, take a cutting or two and try to grow new stock on (therefore if worst case scenario strikes and you lose the original, you will have a new shrub from the parent stock).
- If the shrub was still in the ground when winter arrives and appears to be making a recovery, I would come up with something to protect it through the worst of the winter weather.
