The short answer to your question is "Almost certainly, yes".
The CPS would normally continue with a GBH charge if there was a realistic chance of a conviction. Your brother could be summoned to attend court as a witness. (If he refused to attend, or to give evidence, he'd risk being sent to prison).
Courts can make compensation orders but they might be less inclined to do so if the victim had not cooperated with the police and/or CPS. Additionally, any compensation would only be paid to your brother at the rate which it was paid in by the offender. If the offender was sent to prison he might not be in a position to pay anything at all until he's released and then (if he's on the dole) the court might permit him to pay just a very small amount each week.
A more realistic way to get compensation is through the Criminal Injuries Compensation Authority. The payment then comes from Government funds (rather than having to wait for the offender to pay). However CICA's policy is to refuse to pay compensation where the victim has failed to cooperate with the police. (There has been a recent post, here on AB, from someone who has had their claim rejected for exactly that reason).
Chris