I do not have any experience with baby after pre-e and HELLP (yet!), but I think I am going to be so neurotic that I will want to be seen by both the entire pregnancy, starting as soon as they'll allow it.
I will be seeing a completely new team (we moved states) next time around. If we weren't, I would have been adamant about seeing both anyway because my OB was so lackadaisical and I've developed somewhat of a distrust for OBs. It wasn't until I finally saw an MFM at 18 weeks that he changed my status from "normal pregnancy supervision" to "high-risk pregnancy supervision". My OB knew I had chronic high bp, but never adjusted that. He also kept me on HCTZ and lisinopril until 13 weeks, despite the negative consequences. He never made the extra effort to reach out to an MFM for advice on what medication I should be on. Now, do I think it played any part in what happened? Probably not. But I will feel at ease with an "expert" looking after me.
That being said, congratulations on your big baby and I hope you never reach the point that you need an MFM.