MS SQL 2008 mirroring in WORKGROUP or DOMAIN

Hi,

I am in a weird situation where my customer needs an SQL mirroring solution on new HW, and this config is for end user. But end user is a large company, where all information circle very slow, so they are not yet sure, whether they want this install to be in their AD domain, or should be SQL mirroring stand-alone solution in a small workgroup topology.

Now, my suggestion was to first decide about DOMAIN or WORKGROUP, then we will provide exact plan and offer. But they are in a hurry, offering bids will end next week, and I am not sure what to do with it.

Now, my concern:
What if we install and configure SQL mirroring onto 2 new servers, with additional witness workstation, so everything will work OK in an off-site location...then we move working equipment to end-user's facilities, and they decide that they want to have everything setup inside their local domain?
Ok, there is no need to do DCPROMO in any scenario, but it *might* be necessary to make existing SQL mirroring servers part of local domain. What problems may I expect? What scenarios to assume?

Ideas welcome.