THE MOBILE BASE THAT NOBODY KNEW

I have a chain of questions regarding the special two-turn set-up of mobile bases in the Four Powers War, when nobody had really figured them out yet. Rules (510.21) and (510.22) define the procedure for setting up a MB. Rule (510.232) states that (in combat) if the tug is not with the MB, the MB is considered abandoned. Rule (607.16) describes the scenario rule for setting up a MB as taking two turns for Step 2 (510.22). In my case, a tug which began setting up a MB on the Strategic Move portion of its previous turn, and wants to change missions during the Economic Phase [Step 1F (509.32) Declare roles for tugs] of the current turn.

QUESTION: If the tug voluntarily changes missions is the MB lost/destroyed?

ANSWER: Yes.

QUESTION: Would the MB be considered still 'packed' since it has not been a full turn OR is it considered 'partially set-up'?

ANSWER: It is partially set-up; it has no combat factors, but can no longer move or retreat with the tug.

QUESTION: Then in that 'partially set-up' case, could another tug (assuming a valid SMN) show up during the Strategic Movement Phase of the current turn to complete the MB, basically picking up where the first tug left off?

ANSWER: No, sorry. If the first tug leaves (or is given another mission at the start of the turn), the MB would be lost at that point.
QUESTION: In that 'partially set-up' case, does the interruption of the setup this turn force the process to begin again on the next turn (i.e., a tug could there by strategic-movement this turn but would not be able to continue deployment until the following turn)?

ANSWER: No, sorry. Interrupting the set-up process loses you the MB, immediately. There is no chance for another tug to show up from elsewhere. There is no provision in the rules for one tug to take over the mission of another tug in the middle of the mission, even if the mission takes more than one turn.