By law they have to let you extend your health insurance even if you have to pay more of the premium. As far as them letting you go after you told them you were accepted by another company....my husband was let go immediately when he gave notice. For future reference on your resume you can explain why they let you go. Most companies understand that this happens and don't hold it against you.
I work(ed) for a Board and resigned - giving 2 months notice (that was part of my contract). 4 weeks later the Board fired me - agreeing to pay out the full term of my resignation. They gave no reason (I'm senior management), but it was done in anger. Do they need to give me a reason?