Webber will probably stay for next season, but in 2014, Ricciardo and Vergne will both have had two years at Toro Rosso. I would assume this will be the time where one moves up and the other moves on, they will both be gone by 2015. At the moment it looks like Kvyat and Sainz will be the next in line for those two seats. Unless Toro Rosso is sold, as suggested above.
It will get very interesting at Toro Rosso and Red Bull at the end of 2013. Webber will most likely stay for next year; however, Mark will be 37 by the end of that year, and will most likely retire. Mark is getting old. Vettel has a contract until 2013 for Red Bull, and I remember him saying his dream is to be a driver for Ferrari, but then he recently said he can’t imagine a life without Red Bull. He can’t seem to make up his mind.
In 2014, the most likely scenarios I can imagine are:
1 – Both Vergne and Ricciardo are both very impressive at Toro Rosso in 2013. They both move on to Red Bull while Webber retires and Vettel moves on to Ferrari. Sainz and Kvyat replace them at Toro Rosso.
2 – Both Vergne and Ricciardo fail to impress Red Bull, they are both dropped while someone else fills up RBR’s second seat, preferably Hamilton or Webber might stay for another year, or perhaps both if Vettel does move to Ferrari. Horner feels that the Red Bull junior programme is a waste of time and money, and sells Toro Rosso as the rumours suggest.
3 – One of the Toro Rosso drivers moves on to Red Bull to join alongside Vettel. The other STR driver is either replaced by Sainz and Kvyat, or either one of the young guns is put alongside Ricciardo/Vergne (whoever fails to impress) as a benchmark; or Toro Rosso is sold.