The hour of reckoning is drawing near for Tesla and SolarCity.

Shareholders at the two companies are set to cast their votes Thursday on whether to approve Tesla's approximately $2.3 billion acquisition of SolarCity. It's a deal that Elon Musk says will help both businesses in the long term.

But critics see a host of issues with the merger--most notably that Tesla would be taking on a company that has yet to make a profit since its 2006 founding.

So what will happen come Thursday? Opinions are mixed. Some analysts and shareholders think the transaction benefits both companies; others are more skeptical or oppose the deal entirely. And regardless of sentiments toward the transaction, no one knows for sure whether it will get approved.

Last year, SolarCity lost $768 million and is now about $3 billion in debt. Tesla, meanwhile, just blew past expectations in its most recent quarter, posting $2.3 billion in revenue in its first profitable quarter in three years. The car company has nearly 400,000 preorders in place for the $35,000 Model 3 set to launch next year and, to help it meet that demand, recently acquired German manufacturer Grohmann Engineering to produce more efficient car-building machines.

Combining the two companies, argues Musk in his "Master Plan" outlined in July, will let Tesla create a one-stop shop for solar roofs, solar- and battery-powered cars, and Powerwall home batteries that store excess energy.

Ben Kallo, senior research analyst at investment firm Baird, predicts that despite the obvious financial concerns, investors mostly will be on board, even if slightly more so at SolarCity than Tesla.

"The major thing impacting the transaction being approved or not being approved was showcasing the product," Kallo says of the roofs. "It's important for investors to see that there's some SolarCity technology that will be sold to Tesla."

The solar roofs, which Musk unveiled October 27, received highly positive reviews. They look indistinguishable from regular roofs when viewed from the street; when viewed from above, they're nearly transparent, allowing them to operate at 98 percent the efficiency of standard solar panels. Musk says installations, which will be performed by SolarCity, will cost the same as standard roof installations.

Another factor that could boost Tesla's chances: The company announced a deal with Panasonic on October 16. Under that agreement, the latter company will manufacture photovoltaic cells for Tesla at its Buffalo, New York factory--contingent on approval of the Tesla-SolarCity merger.

Those recent developments have convinced Kallo, who pegged the odds of an approval at 50-50 back when news of it was first revealed, that the deal has a 90 percent chance of receiving the majority vote needed from both sides.

Advisory firm Institutional Shareholder Services, meanwhile, recommended in early November that both companies vote yes. That surprised even Musk. "I thought they wouldn't recommend us, but they did," he told CNBC. "They tend to be a bit negative."

If Musk is looking for negativity, though, he hasn't had to look too hard. Jim Chanos, founder of advisory firm Kynikos Associates, referred to the deal as a "brazen Tesla bailout of SolarCity" back in June. Corporate governance expert corporate Charles Elson called it "about as clear an example of conflict of interest as I can think of."

CTW Investment Firm, which holds 200,000 shares of Tesla, echoed those sentiments. The company sent a letter to Tesla--which went unanswered--soon after news of the SolarCity proposal became public, requesting that the company create a special committee to review the deal. In addition to Musk being co-founder and major shareholder of both companies, he's also both chairman and CEO of Tesla. SolarCity is headed by his first cousin, Lyndon Rive. The company's board of directors contains many of Musk's early venture capitalists, as well as his brother, Kimbal Musk.

"If you look at Tesla's board," says Etelvina Martinez, corporate governance manager at CTW, "all of the directors except the newest member have some sort of connection to SolarCity." Investor Antonio J. Gracias, for one, serves on the board of both companies; Tesla board member Brad W. Buss was SolarCity's CFO until he retired this February.

Martinez says CTW hasn't taken an official stance on whether or not the deal is a positive for Tesla, but she has concerns about the board's ability to be impartial, as well as whether the company explored other transaction opportunities deeply enough before deciding to pursue a deal with SolarCity.

"You have this board that's been around Elon Musk for a long time, so I don't think there's enough independence to really challenge him on decisions like this transaction," says. "We just don't have any indication that there was enough pushback."

Others think the deal might make sense down the road, but say right now is too soon for Tesla to acquire SolarCity, which hasn't yet proven it can sustain itself in the long term.

Musk disagrees. "I think the timing is just right, if not, I mean frankly, we may be a little late. I wouldn't say that we're early," he told CNBC earlier this month. "It is really an accident of history that the companies are even separate."

That's a narrative Musk has been trumpeting since this summer, when his master plan, which alluded to an eco-friendly future of solar roofs that power electric cars, declared that the companies should have been one entity since the start.

It's a romantic thought for Musk and his supporters, of which there are many. Unfortunately for him and for them, there are also plenty of shareholders who don't agree. Some of Tesla's shareholders were so against the vote that several filed lawsuits against the company back in September trying to block it, prompting the vote to be pushed back.

Technically, they have been able to cast their votes since September 23. The majority of the votes will be cast by proxy: Shareholders send their decisions by mail and allow a representative to vote on their behalf.

So what happens if the deal doesn't pass? SolarCity likely has more to lose from a no vote, given Tesla's recent turn toward profitability. The companies could still work together and feed off each other's technology even if they're not one company, but Musk has argued the operation likely wouldn't be as efficient as it could be. The companies have said they'll save $150 million in combined operating costs in their first 12 months after a merger.

The votes will be cast in California at 11 a.m. pacific. Stay tuned for more on the fate of both companies--and Musk's master plan.