Unfortunately, it's unlikely they will get their jobs back if Uber fails. The world simply doesn't work that easily. The market had a certain demand for taxis before Uber existed. If Uber never existed that demand today would be different, but it would not be the same as it as today because... Well... Uber exists and has changed a lot of aspects of the industry.
If Uber fails then, as you said, some of the market would go to Lyft and other companies that provide the things users have grown accustomed to with Uber (eg phone apps and not being seen in a yellow cab). But it won't go back to how it was before and the population of taxi drivers who lost their job and are unable to drive for Uber, Lyft or one of their competitors are likely close to unhireable for whatever reason.
However there is a generation of folks who would never drive a taxi but will drive for Uber in their free time and those people likely would have gotten different jobs if Uber didn't exist but now may have more trouble due to age, experience, flexibility, whatever. There are also far too many people who have purchased or leased cars they otherwise wouldn't have, and that changes things as youre not going to drive your new Prius when you're a cab driver. So you're going to pay off that lease for the next few years while it stays in the driveway and you drive a yellow cab? Oops.
I am not a huge fan of Uber. I've never actually gotten an Uber from my phone. I've been in Ubers. We use them internationally. But when I'm alone, finding the yellow cab or taking the metro or walking home is simply what I choose to do because it's rare I'm alone in an unfamiliar place and I've been taking cabs since I was 14.
What I dislike about how Uber entered the market was that they completely and utterly failed at scaling and their obligations to society and building a viable business. You cannot cut out all costs that you will have to deal with at some point when the laws catch up and use those unrealistic numbers in order to take more funding. That's not genuine. And then instead of.. You know... Using that funding to balance out the discrepancies, they've used it to lobby in pretty much every country and in a lot of cases it didn't work out.
Furthermore, instead of continuing to ramp up in a somewhat responsible manner, they took this route of crazy stupid more than exponential growth. If you look at the graphs it's ridiculous. They were only able to do this by completely ignoring the rules and taking money that only exists because we're in a bubble. Some rules are antiquated and decrease market competition and I care less about. But things like not paying their drivers anywhere close to minimum wage, ignoring regulations that actually do exist for a good reason, and using that not-so-hard-earned-valley-money to lobby doesn't build a sustainable business that does anything for the world around it.
Uber should not exist in the form it does now. Period. And they will fail - slowly, quickly, or somewhere in between. And their growth and subsequent demise will be felt by a lot of industries for years to come. Only one if their problems is an incompetent CEO and the shitty culture he's built.