Webber will leave F1 at the end of the season to drive Porsche's LMP1 entry (with Dumas/Bernhard and an RB test/sim driver). I wonder if Prosche has lined up RB as a sponsor for their LM-entry. Although it wouldn't be their style, and LM is somewhat less sponsor heavy (and more works focused in LMP1) than most other motorsports, fetching two RB drivers, and the lack of RB involvement in LM could mean something.
Anyway, I think it's high time that Webber left. He was the experienced driver RB needed when they turned around Jaguar into a winning team, but they probably want someone a tad faster, now that Vettel has enough experience to be trusted as a development driver.
The real question is whether RB will go looking for a number 2 driver, or someone that will race Vettel, like Webber did when things were going well for him. Essentially - will they promote someone from STR, or get someone like Raikonnen. I suppose they don't know themselves yet...