Youtube monetisation isn't great, not a lot of money can be made. A lot of Youtubers will normally look at other avenues (once they have built up a good base of subscribers) such as sponsorship, advertisement or collaborations (like Zoella wrote a book and developed her own beauty range - nothing amazing but a lot of her subscribers bought into it). A great deal of Youtube success depends on the content, what your target viewer is and the quality and regularity of your videos. It isn't easy to achieve success. For some vloggers, they can spend a great deal of time filming, editing and uploading videos with not much reward or views. If you have your heart set on a Youtube career, I would do it alongside your day job, so you have something to fall back on if it doesn't go to plan.
In terms of finding work after a failed Youtube career, it depends on their job experience before. Youtube wouldn't really contribute much, you could say it was creative expressive outlet for your passions and it shows you can use social media, but that alone won't guarantee you a job.