The Manchester-based B742s still belong to Virgin (as do the 3 ex-ANZ machines still in the desert), and are leased to Air Atlanta Europe to be operated on their AOC on Virgin's behalf (the B742 is no longer on Virgin's AOC). The aircraft are crewed by Virgin cabin staff and some Virgin, some AA flight deck. They are scheduled to be replaced by 744s over the next year or so, probably at the same time as Virgin plans to add further schedules from MAN. As I believe Virgin Holidays is the main customer for the BMI Caribbean schedules due to start shortly, I'd guess that these are the routes Virgin is looking to operate from MAN.
As for new destinations from London, Nassau and Havana are likely to be operated from Gatwick. Rio (if it happens), Dubai and Toronto probably would be also. I imagine that the VS5/6 Miami would return to Gatwick to free up slots for Chicago and any further Bostons - though there was talk last year of operating LGW-BOS. SYD is to ride the back of the daily VS200 schedule for now; there are no current plans to add a second HKG. Mumbai, like Delhi, may be operated on behalf of Air India using their slots.
There is no definite news about A343s being retired. At the moment, the company seems to wish to keep the 9 remaining aircraft.