Take these answers with a grain of salt, but I'm pretty sure they're correct.

When a ninjas dies and is revived ALL buffs are reset to nothing, whether they be scaling or otherwise.

When a scaling ninjas is buff cleansed (or whatever you want to call it) by Han or similar, then I'm fairly certain the scaling stays where it was and is not reset. I say based on experience with ninjas like kimmimaro that I have dusted late in a match and still take the same amount of damage immediately after, indicating his def scaling was still active. It is also possible that this has been changed in recent updates, I haven't really tested such a thing since 3.0 came out, since it's been quite since I looked into it.