That depends on whether it was 1st or 2nd degree robbery; punishment for the former is 3, 6, or 9 years in state prison, for the latter 2, 3, or 5. Before you panic, if he was a juvenile when he committed the offense he may not be prosecuted as an adult, depending on his age at the time of the crime. It is also possible that if the 211 is very old the statute may have run. the escape complicates things considerably. He needs to consult a criminal lawyer specializing in juvenile problems.
There are two issues that your boyfriend needs to address. The first is what the juvinile court is going to do because he did not complete his "year placement." That could vary depending on how long he did before he ran away and - maybe more importantly - what court he is in and who his probation officer is. The other issue is whether or not the DA is going to file additional charges related to the "running away."
The best tactic for your boyfriend is to talk with a qualified criminal defense attorney in a confidential meeting. Anything said in that meeting is private under the attorney/client privilige. At that meeting, your boyfriend can freely talk about his case and all the facts related to the "running away" and the best strategy for dealing with case can be made.
Your boyfriend should know that he simply can't run away from juvenile court. Even though he is an adult now, the court retains jurisdiction over him if a warrant was issued. If he does something really stupid while he is out, he can be sentenced to the Youth Authority since robbery (assuming no firearm or weapons) is a 707(b) offense up to age 25. A person can be held past age 25 only if they are deemed to have difficulty controlling their dangerous behavior (see WIC 607 & 1800)
The advice that you have received thus far is very good and you should instruct your boyfriend to follow it. As others have suggested, your boyfriend should consult with a criminal defense attorney in his area that handles juvenile cases. Good Luck!