With barely any time until Sochi, the typhoon still at large affecting travel preparations, plus all the emotional trauma (We don't know yet that poor Jules will pull through) I think there's a good chance that it will just be one driver at the next race. But they WILL race, as they have to from a financial aspect and Bianchi wouldn't want the team to suffer because of him.
It will be interesting to see if Bianchi's seat is the only one that needs covering. Things like this affect people - will Felipe Massa who is at Bianchi's bedside, be in a fit state to race, for example, especially if Bianchi's fight goes on (whichever way) for a few days?
If they have to name someone at short notice, then it will likely be someone who has been in FP1 this year - Rossi being the most obvious. But due to Bianchi's links with Ferrari, I wouldn't be totally surprised that for the latter races of this season, someone like de la Rosa fills in.
That said for someone like di Resta, who is rapidly being forgotten about in F1 terms - something like this would be an opportunity. He's arguably the best ex-F1 driver of the last 12 months to be available.