Since both Solar City and Tesla are burning cash right now, I highly suspect Solar City is going to face a massive layoff of their sales staff and massive cut to marketing, which is where a majority of their costs are right now. With that gone, Solar City might be profitable, or at least close to break-even, based on existing solar installs.

That's what Tesla is probably hoping for anyway, I highly doubt it will work out quite that nicely. This seems like a highly risky acquisition from a financial perspective for both companies.