SolarCity is a pretty worthless company, in my opinion. Solar panels can be made cheaper by regular competition and there's no need for a car company like Tesla to build them themselves.
Elon wants to own a solar company, despite not spending much time on it at all, and so think of that 2B purchase as money down the drain for Elon. Its common to make $200 million a year for a top CEO, that's 5 years salary for someone like Elon. Since he only makes 5 million, thats fine.
It is an LLC, so that means if they go bankrupt, it won't affect Tesla more than what they paid for it. They would look bad, but won't go bankrupt from it.
The service is no doubt bad, but there's nothing to redeem them like there is for Tesla. They just make solar panels like everyone else does. So far as we know, they've got no special technology nor are they very good at anything.