cockpitvisit
I thought the crew would be heading to a hotel for a rest period, instead of immediately operating the return flight. This would give Virgin plenty of time to fly in a replacement crew.
Obviously that's not why VA returned last night but as a generic reply to your comment ( because the principles apply if for example somebody falls ill downroute):
How quickly can you get a replacement, perhaps from home, into the base airport (2-3 hours)?
What's the delay until the next available outbound flight departs: Later same day- 2-3 hours+? The next day A.M.- 8-10+?
What's the flight time base - destination (e.g. LHR-JFK, 8'ish hours) ?
How long a rest period is then needed post positioning before operating back?
(may be 11-12 hours at hotel, depends on the rule set )?
You can do the sums, but unless you're lucky you almost certainly won't have "plenty of time".
TBH I've usually found that if things go wrong downroute on a <=24 hour slip that unless the company can re-jig the trip of a suitably qualified pilot
already at that destination and switch him/her onto your trip you'll usually have a delay.