I think approval is highly likely. The key is going to be usage - the drug is clearly better than Flagyl and equivalent to vanco from an initial efficacy standpoint and better than vanco from a recurrence standpoint.
However, Flagyl is dirt cheap, and vanco at some point will be generic - even now many hospitals compound it for oral use rather than pay VPHM's ever-increasing prices. So is OPTR going to charge vanco prices ($1k), even more (like $2k) or something more reasonable? At the high prices they will only get usage for patients with recurrence. It's instructive how widely used Flagyl is even though its efficacy is clearly worse than vanco - so that is an indication of the price sensitivity of the market.
Personally I think that if you look at all the costs involved it might turn out to be cheaper to use Fidaxomicin at the outset even at a high price - there will be some outlier cases with dramatic costs (like $100k or even more) for the folks they start out on inferior treatments like Flagyl. But short of a full pharmacoeconomic study it's hard to make the argument convincingly.