Webwork - 5:26 pm on Jan 18, 2013 (gmt 0)
1 vote for subdomain. Alternative would be subdir. Selling off the B&M store complicates things a good deal since there are multiple legal, branding and competitive issues.
IFF the breakup is a certainty, not just a good idea, then it may more more sense to go with 2 domains/sites, to separate corp., separate accounting, etc. in order that a substantial portion of the groundwork for the breakup is already in place.