.net – How to automatically re-establish a duplex channel if it gets faulted

You should keep the client side proxy open while you wish to receive callbacks and when done you should close the channel.

Here's a quote from the great book Programming WCF Services by Juval Lowy (I suggest you to read the whole chapter about callbacks):

5.3.4. Callback Connection Management

The callback mechanism supplies nothing like a higher-level protocol for managing the connection between the service and the callback endpoint. It is up to the developer to come up with some application-level protocol or a consistent pattern for managing the life cycle of the connection. As mentioned previously, the service can only call back to the client if the client-side channel is still open, typically done by not closing the proxy. Keeping the proxy open will also prevent the callback object from being garbage-collected. If the service maintains a reference on a callback endpoint and the client-side proxy is closed or the client application itself is gone, when the service invokes the callback, it will get an ObjectDisposedException from the service channel. It is therefore preferable for the client to inform the service when it no longer wishes to receive callbacks or when the client application is shutting down. To that end, you can add an explicit Disconnect( ) method to the service contract. Since every method call carries with it the callback reference, in the Disconnect( ) method the service can remove the callback reference from its internal store.

Actually, although I blogged (see Luke's answer), I think this is better than my IDisposable wrapper. Typical code:

Service<IOrderService>.Use(orderService=>
{
  orderService.PlaceOrder(request);
}); 

(edit per comments)

Since Use returns void, the easiest way to handle return values is via a captured variable:

int newOrderId = 0; // need a value for definite assignment
Service<IOrderService>.Use(orderService=>
  {
    newOrderId = orderService.PlaceOrder(request);
  });
Console.WriteLine(newOrderId); // should be updated