How are the roots? The plant will have a better chance of recovering if it has a strong root system. If it doesn't have many good roots, you could try soaking it in a rooting hormone, like K-L-N. I've also heard very good things about KelpMax or similar seaweed products. I only just got KelpMax myself, so I can't say from experience yet how good it is, but from what I hear it can make a huge difference!
Best of luck to you. It sounds like this plant is really special, since it belonged to your granddad
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Keep us posted!