Elon Musk reportedly worked as many as 100 hours a week during strenuous times at SpaceX and Tesla Motors (NASDAQ:TSLA) -- two companies where he serves as CEO. While he said in 2014 he had scaled back to an average of 80 to 90 hours a week, it bears wondering whether the entrepreneur can sustain his dual CEO positions for much longer.

Elon Musk.

This is a key concern for investors of publicly traded Tesla, as the CEO is arguably just as important to the electric-car maker as Steve Jobs was to Apple. If Musk were to step down, investors would likely be worried the company may not be able to accomplish its wild aspirations.

Fortunately, while the CEO admits he is only 100% committed to remaining CEO of Tesla through high-volume production of its mass market car, or the Model 3, he does promise to stick around in other capacities as far into the future as he "can possibly imagine."

Musk's long-term plans for leading Tesla
It's not news that Musk has only promised to remain CEO until a ramp-up in Model 3 production, which the company expects to occur between 2017 and 2020. This notion started making rounds in the media in 2014 after the CEO said during Tesla's annual shareholder meeting he planned on keeping the role for four or five years -- or at least until Tesla ramped up production of Model 3.

Musk seems to simply be acknowledging the obvious: Running both Tesla and SpaceX as they continue to grow probably isn't sustainable.

He has said he wouldn't wish his current workload on anyone.

"I wouldn't recommend running two companies," Musk said during a Vanity Fair Interview, referring to Jack Dorsey's recent decision to be the CEO of both Square and Twitter.

A serious commitment
But Musk's commitment to Tesla goes much deeper than his oft-cited references to sticking around until Tesla brings a mass-market vehicle to market. Consider these quotes from the CEO:

"I'm always going to be involved with Tesla -- I mean -- forever," Musk said in a CNBC interview in October 2014.

He continued:

The only question is whether I will be CEO forever, or at least until I die, you know. I'm committed to be CEO at Tesla through volume production of the mass-market vehicle, but I will continue to be involved with Tesla as far into the future as I can possibly imagine.

And when MarketPlace asked Musk in an October 2015 interview what it would take for the CEO to stop day-to-day management at SpaceX or Tesla, Musk responded saying he expects "to be with SpaceX and Tesla for as long into the future as I can imagine."

Rendering of Falcon Heavy, a rocket equipped with three of SpaceX' reusable first-stage Falcon 9's. SpaceX' mission of enabling people to live on other planets is arguably more ambitious than Tesla's goal to accelerate the advent of sustainable transport. Image source: SpaceX.

Chances are, Musk will also keep his chairman role for a very long time, too. Musk owns about 27% of the company, continues to buy stock, and even promised in 2013 he would "be the last one to sell shares."

It's good news for investors that Musk plans to stick around at least in some capacity. The CEO's hands-on role, which includes 70% of his time being devoted to engineering and design, wouldn't be easy to replaced. And with Tesla's growth accelerating recently, the co-founder's vision and zeal is arguably as crucial to Tesla's execution as ever.