It will be plated - there is no way they will go back to expensive Silver Service. No idea re tips as 2009 has not happened yet !
Re the tipping. I understand that if you are on Freedom Dining then there will be an automatic tip charged to your account to take heed of the fact that you will not have the same waiter two nights running. If you are on Club Dining then you tip as you wish at the end of the cruise. Of course you can alter this by speaking to Reception but it is difficult to be fair as you do not have the same waiting staff if you have Freedom Dining. Last time we were on board Oceana the meat, potatoes and one vegetable was plated and the waiters came round with more vegetables. I don't know if this has changed.
P&O quote in their 2009 1st edition brochure that freedom dining and club dining have silver service in the main restaurants.