I think Vionnet would be a difficult house to revive as far as couture goes, simply because Vionnet is a name synonymous with a certain era, a certain type of clothing, a certain look, and a certain construction technique.
When you say Vionnet, I automatically think of slinky, bias-cut crepe column dresses from the early 1930s. I know Madeline Vionnet worked in the 1920s and maybe in the early '40s as well, but her best and most famous work was in the 1930s. Her greatest successes were in afternoon and evening dresses; semiformals were her greatest strength, though she did put out a few truly stunning, show-stopping ball gowns.
There is too much history, too much weight behind the Vionnet name. Anything that didn't adhere pretty strictly to Madeline Vionnet's original style would seem almost a sacrelege, but fashion thrives on the new. If a talented designer could rifff off of the old designs and bring them up to the 21st century, it would be marvelous and cool, but I have a hard time imagining it happen.
I think Fath could pull a Balenciaga. They were two somewhat similar houses back in their day, and I think the experimental, achitectural, artistic approach could be revived for Fath. Back in the day, Fath's designs were more wearable than Balenciaga, and I think it would be appropriate to revive Fath in a similar vein; fairly avant garde, but not completely removed from the reality of human bodies and daily wear.