I share your concerns here and in fact have been trying to dig up more on this.
Here's a quote from a message sent to me from my lawyer:
To respond to your concerns, your status is that of a pending adjustment of status applicant. It sounds odd simply because INS has not given that status a formal name; rather, through a collection of regulations and policy memoranda, the INS has recognized that individuals whose applications for adjustment of status are pending are entitled to live, work, and travel in and out of the U.S., and do not accrue unlawful presence while their applications are pending. Accordingly, once your AOS is filed, it is not necessary for you to maintain your nonimmigrant status (e.g., H-1B, H4, etc.), though you may do so.
I assume that the part of the statement about work and travel implies "if AP and EAD have been obtained"
From what I have been able to uncover myself.
1. I-485 applicant can stay in the US and not accrue unlawful presence, as deemed to be present in the U.S.
pursuant to a period of stay authorized by the Attorney General(
http://www.lianglaw.com/INS/law-data/HQADN70.21.1.24-P.htm) This one is pretty old, but I've been told that the new ones look similarly.
2. Although I-485 keeps you in status, it doesn't undo all previous unlawful presence or employment (if any ) - so - ironically - AOS applicant can be deported based on that. Until recently it has been never done - especially if filed under 245(i), but several weeks ago INS seemed to try to use it to deport people that showed up for Special Registration. That varied from office to office and most of them have been released... but anyway, this issue is very tricky.
3. Filing I-485 declares you immigration intention and therfore voids any non-immigrant status you had. This
excludesH1-B/L holders who may choose to maintain their non-immigrant status, although this is not necessary. This link discusses issues related to that (
http://www.shusterman.com/hl-99regs.html ). Overall you would only maintain non-immigrant status if you're afraid that I-485 will be denied - it doen't seem to matter otherwise.
4. The expired I-94 seems to be of no consequence for your current status, with the exception that it serves as proof that your I-485 was filed when in lawful status - see 2.
5. Unless H1-B/L is maintained, EAD is required to work, AP to travel. AP holders may not be admited back to the US if certain unlawful presence been acrued ( see INS memo
http://www.ins.gov/graphics/publicaffairs/advisories/02.11insissu.htm )
6. Important : you can either work/travel under H1-B/L or EAD/AP, but not at the same time. In fact, the moment you use either AP or EAD, H1-B status is deemed void and only EAD/AP can be used form that moment on.
This is about it...
In your specific case, when you said that you "had" EAD... has it been used? If so, no, you can't go back to H1-B( and I don't see why you would anyway ). If it hasn't been used, you may keep maintaining your H1-B status.