Once my mom returns from rehab is that my lot in life?

MidKid58 has a good point, because children really are stressed when grandma is withering away in the middle of what used to be a dining room or family room. Even a three year old senses something terribly wrong is going on. You will see tantrums, refusal to go to bed, picky eating and a lot more. Start thinking nursing homes..

I would be working on placing her in a care facility, That probably isn't what she wants, but no way you can care for her, your kids and work. You'll last 2 weeks and have a meltdown.
Also--nobody ever mentions the kids who still need a healthy mom!! My FIL was dying and my hubby wanted him to die in our home (with me caring for him 24/7) My kids were 18 and 15 and they BOTH said they would move out if we moved him in. They had rights, too. The right to not listen to a dying man gasping for air all day and night. The complete disruption of THEIR lives at a crucial point. I ended up taking care of him at his home for 6 months (3xs a day visits) until her died. A lot of stress and work, but better for the family.

start now working with the hospital social worker and rehab center to let them know she will not be able to be cared for at home. They can help identify where she can be placed. You can still be her loving daughter and advocate. Don't let yourself sacrifice your kids etc to becoming a 24/7 slave - i'm sure your mom wouldn't want that for you. Let us know how all turns out.