Six weeks ago I bought a new 2004 XC90 T6. Yesterday, with just under 2K miles on it, the car died while my wife was driving it on the highway. It turns out that some screws had come loose and all of the transmission fluid leaked out, causing the engine to shut down. The Volvo dealer nearest the breakdown (not where I bought from) has fixed the problem, and says that no damage to the transmission can be seen. What I need to know is, 1) Is it plausible that there was no damage from such an event? and 2) If damage is likely, what are my options?

Many thanks in advance for any thoughts and advice.

Unbelievable!
I would be very concerned about potential damage regardless of what the dealership assured you, if indeed ALL the transmission fluid was drained. Secondly, I would insist that your place of purchase, put in writing an incident report, signed by them, that can be used in your favour in the event of a total failure of the transmission during the warranty period.