Sometimes it's the exact same product, but with a different name.

That's basically what zmud/cmud was. He basically slapped a different name on a major update and declared that since it's a different product it requires a separate license and the old product would no longer be updated.

No need to kill the old product if you just let it stagnate. Things like OS updates and providing no support will slowly kill it for you, without you generating the ill will of prematurely killing lifetime licenses.