i'm thinking what kind of idea i could plant before i die, because our idea itself is immortal.

You nailed it. We all have our time to do our acts. But after an act is done nobody can change the fact that it happened. At best a person could undo the effects of an action. A great idea to spread is,
Do no harm
Do good when you can
Get smart. Get really really smart to know which is good and which isn't.

Thanks for commenting :-)