I don't think the plant will be stable in the future. Consider restarting it from a cutting. Avoid touching the sap if you go that route (potent irritant). This Euphorbia tends to grow weak and lanky indoors, due to insufficient light. The more light, the better in an indoor situation. Obviously you've been taking great care of your plant if you've kept it alive and looking that good for 10 years inside, there are just some inherent limitations with the plant.
