What do you count as "not really being decentralized"? It is unlikely that there will suddenly be hundreds of trusted server operators out there on the same day that it (supposedly) is open sourced... Currently there are a low 2 digit number of rippled servers running of which only the minority is operated by OpenCoin. Is this enough for you (and at which point was Bitcoin "really decentralized" by the way?)?
Simply put, can the Ripple network continue operating without OpenCoin?
You have to understand that Bitcoin's biggest innovation is that it can establish a consensus without any centralization; the blockchain is the authority, etc. If they release a passive daemon, it is interesting for developers, will likely create many gateways, but still would have a single point of failure.
It already could, as there are more non-OC servers in the network than OC servers online. Most of them probably use OC servers exclusively in their UNL though, to ensure that any needed changes actually are accepted until opening up.
Ripple is already now able to establish consensus without any centralization, the only reason it maybe (I can't tell which UNLs server operators are using) does still trust OC to a degree that it could be called "centralized" is that there could still be changes to the protocol that need to be done and that would be hard to do in a decentralized way if the operators of servers operate them in a "fire and forget" mode or start actively forking and/or testing the network.
Ripple is secured by having a diverse UNL (Bitcoin by computational power of miners), so the biggest issue that needs to be solved still imho is how to actually build a good UNL with trusted, non-colluding entities asap after going live.