Tesla's "autopilot" was too much, too fast. It's not very good and was promoted as being more capable than it is. Tesla really needs to enforce hands-on-wheel strictly.
The Tesla Model 3 at $35K with big production volume is a big risk. It will probably come out late, at $50K+, and in lower initial volume. But it should make it out the plant door at some point. That's the biggest risk item in all this. Remember that when Musk announced the proposed Model 3 production schedule, the two top people in production quit. They clearly knew the goal wasn't realistic.
Tesla buying Solar City looks more like a bailout. The big Solar City risk is that they're building their own solar panels. They could be undercut by competition from China, as Applied Materials was. Solar City has the advantage that their plant sells to themselves, so they can resist competition to some extent. Solar City's big vulnerability is that they're heavily dependent on Government subsidies. Those are gradually going away as solar becomes able to stand on its own.
The big risks are financial, not technical. Hence the pressure at Tesla to cut costs, and probably use creative accounting, to get a profitable quarter.