I don't see this debate as happening if they were demanding one before the April 24th races then perhaps. In fact that would be their smarter move.
If Romney rolls every state in April he is going to win NC, Oregon, Indiania and West Virginia. The only that could be in play for Santorum I suspect are Kentucky and Arkansas given the high evangelical population they have.
West Virginia is not Romney country at all, demographically. It's one of the poorest states in the country, has a very low percentage of college degree holders, and you know Santorum is going to basically walk around with a "MY GRANDDADDY WAS A COAL MINER" sign around his neck up there.
But at the same time, the only Republicans who get elected there tend to be moderates (Shelley Moore Capito), and they have a history of voting for wealthy blue-blood types (Jay Rockefeller, Gaston Caperton, etc).