They own a percentage of Newport-Gwent Dragons (I think) so couldn't see them leaving or being allowed to leave. As for the rest regardless of the threats you'd imagine that there would be some serious legal ramifications with that decision but I don't think anyone could give you a definitive answer.

No way that the French will be interested in joining a Pro12 type league I think. Personally I think that the WRU need to take that last step and bring a couple of "real" Welsh clubs in if that happens. Pull all of their support out of the RRW and throw it behind any new entrants (this time they need to buy a "share" of the club in return for their money).

It may or may not happen or be allowed to happen, but assume for a moment of the doomsday scenario that the Welsh Regions are allowed to, and pull out of the Pro 12 and join the English premiership. What then for Pro 12?

4 Irish clubs, 2 Scottish (both sponsored by BT Sports) and 2 Italian - not an enticing prospect. Plus a SKY deal, but without a sponsor.

Could the 8 play 3 matches each, so 21 matches in the season?
Would the WRU add in two or more clubs EG Pontypridd, Newport (essentially AIL type clubs)? Is there an opportunity for an extra Scottish club (Borders)?
Would the standard be too diverse to get a Romanian club or another Italian club?
Could the Pro12 be merged with French leagues to complete a Euro type league? Would other French clubs allow it or welcome it? I would guess the fans would welcome it.

Interested in Clan thoughts, 'cos I have absolutley no idea!