Domain Migration Question

[DRSearchEngOpt]

Lets say there is a brand that has one primary product type at different optional tiers. (Think something like SMB/Enterprise/Individual) Lets also say that 1 year ago this brand migrated from having everything under 1 domain (Domain A) to moving 2 of their product tiers to another domain (Domain B), a new domain.  They have done some initial SEO work on this domain and had a pretty successful migration but it has also been decided that they are going to no longer offer one of these product tiers and they intend to eventually migrate everything back under the 1 domain (Domain A)  They just are not sure whether they should do this now or later.
During this next year or so there is also going to be some likely re-branding/design, etc...stemming from this decision, on the domain, meaning content changes and all that fun that goes into a migration/re-design/re-branding strategy. The timing of this has not been fully decided on.

Here is the question:

Should they a) Migrate back to Domain A first and then do the re-design or b) Keep 2 separate domains for now, figure out the re-design/re-branding, make content changes and then migrate Site A over in a year or so after all changes have been made?

My concern with option a) is that they migrated a little less than 1 year ago and will be migrating back which I feel could have a negative impact on the content and the domain.  The positive side I see here is that this impact could be just as large even if we waited so doing this now might be a better, more efficient use of our time if we can migrate and make content changes fairly close together or concurrently.
My concern with option b) is that the tier they no longer offer makes up the majority of that sites business and traffic, leaving us with not much in terms of content that ranks well and garners much traffic.  Trying to optimize for the remaining product tier by itself on it's own domain could be quite hard and then having to migrate it in a year or so back to Domain A could negatively impact any small organic impact I can make on applicable pages/domain.

Does anybody have any input here?  I am leaning towards Option A and but wanted to get some other opinions.

Thanks Everybody!

Edit: So far, this has received a lot of views but no input.  I am hoping to have a bit of a dialog on this so any ideas or input is welcome.

[NickLeRoy]

The question that isn't being asked here is if rebranding to establish a brand is the better play.  As you are finding out, when you register domains and build out sites determined by your offering/product your site is a bit limited.   So why not reconsider the rebrand with a new domain that doesn't put you in this situation again.  Then you'll of course want to migrate the appropriate content add the 301 redirects etc.

Good Luck