I was working at a job making 3 times what I do now as a student and it was great! No doubt it's hard to go back! But, like my peers who were also working, there are two major reasons to leave:
1) Timing. If you are flexible now, no spouse and no kids, then GO WHILE YOU CAN. We all know lots of people who hear that we are going back to school and they say "yeah, do it now while you can. I wish I would have gone but now with the family..." Being broke is not so hard when you don't have to answer to anyone.
2) Career path. Eventually many of us will tap out on the career ladder without the degree we need. That is why we are looking at grad school in the first place. The job market is getting more and more crowded and sometimes we need the right background to be really good at out work. I came because I needed the knowledge base I'm getting. If it's a choice of going now or hitting a glass ceiling and going later, now seems better to me.
It's hard to come back and be broke, but it's also fun. You won't be going to fancy restaurants and you may have to live in shared housing. That's life! Just have a good attitude about how ridiculous it is and find some previously employed students to commiserate with. Being away from work has actually been really helpful for re-grounding me and giving me space to ask big questions about what I want out of life. And it's exposed me to a bunch of new opportunities. You'll be broke, but you don't have to be miserable.
And hey, it's always fun to have a laugh at the kids who are in the program fresh out of undergrad and living at mom and dad's. They are so easily impressed by our financial planning and tastes