You can spin off a plan - that is, split a plan into two or more pieces, regardless of any changes or lack thereof to the sponsoring employer. The new plan, for the division being sold can then be merged into the buyer's plan. However, if those employees are terminated from B, you can distribute according to elections or possibly do a trustee to trustee transfer w/o the administrative hassle of a spin-off merger. Also think about vesting for these employees, which might need coordinated effort/agreement between buyer and seller if full vesting is desired or non-vested balances are to be transferred as well, and then there's the possible partial termination. I'm sure others in this forum who deal with 401(k)s more than I may have further insights.