As a computer science engineer in the field of consumer products, I would be extremely skeptical about the concept of "griefbot". As a matter of fact, there are so many negatives and downsides in such a proposition I would strongly advise against it. Some that come to mind in random order:

• the griefbot is not the real person, so the whole idea is just like chatting to a random machine
• chatbots are terrible at interaction. No really, they may talk good for a while, but down deep they suck.
• there's so much more to a person than the sum of their "collectable data"
• the idea alone of building a bot that, knowing data, can mimic a person, is plain delusional
• weak subjects could have terrible side effects: addiction, emotional breakdowns
• the bot, being an AI, is fundamentally unpredictable (unless it's plain simple stupid) and could easily derail towards the representation of personality disorders: would you like to talk to a machine that pretends to be your dear departed but is actually a manipulative sociopath that does not give a damn about you?

In short, BAD IDEA. STAY AWAY.