Leaving job after FMLA leave?

Hey all- my 12 weeks is up April 10th. Due to virus my first day back will be the 13th (provided they don’t furlough). I have a very toxic boss who harassed me my entire pregnancy about time off etc. she is just extremely rude and even told me I have no empathy when I was 8 mo pregnant. Needless to say, I’ve never cried more in my life than at this job. The plan is to go back, however, I may have a new job offer coming that I would not be able to refuse. They are aware of my current leave and wanting to give 2 weeks notice. I do not have insurance with work, and my disability plan is through a separate company. Any experience with going back for 1 week and giving notice? Experience? I have anxiety, so of course it makes my nerves uneasy. My pay was strictly my PTO/sick time and disability was paid by 3rd party that I pay a premium to. I just don’t want to be stuck paying them for something, especially after being treated so shitty. And I’m sure, the shorty treatment will start again upon return :(