If the tenants gave 30 days notice and have met all of the requirements in their lease, they should get their deposit back as well as any rent due. The management co. sounds a little scummy for keeping your management fee right here at the first of the month, but their/your rights in this matter probably depend on the contract you signed with them.
Sounds like you should be glad you're taking over management of this rental yourself! You need to jump in there and see that it's cleaned up, change the locks, and ready to re-rent. And get some ads run in your local paper and American Classifieds. And put a FOR RENT sign with your number in the front yard.
I don't know how things are done in SoCal, but that's what I'd be doing here in SW Okla. And I'd ask every caller, "Would you like to see it?" as soon as I've finished describing it to them. I get the impression that you're gonna be strapped for cash this month if you have to make this mortgage payment yourself?
Again, I don't know your locale, but here, rental owners joke about needing to have at least 6 rental units (and 8 or 10 are even wayyy better) before we can breathe easy if one comes open and we don't immediately re-rent it. Or if, God forbid!, tenants trash a place and we have to go in to do a few thousand dollars worth of remodeling. Good luck to you!