How has the Wollemi Pine faired through this last cold winter

It seems in general that the trees need to have -12 to -15 degrees centigrade for fairly long periods to actually kill them (as seen in central Europe in the winter of 2010/11). There have been a handful of reports of trees not surviving this last winter in the UK but on investigation this has been in the main due to the trees already suffering from a fungal root disease called Phytophthora which is a wide spread and very common disease with the ability to affect many garden plants. A simple investigation should give some clues to the demise of your tree. Make a small 'nick' in the bark at the base of the tree and if there are signs of healthy white wood and greening on the inside layer of the bark it could be that the roots are still alive. If there is no sign of life then lift the tree and look at the roots they will be dark brown and there is unlikely to be any white or light brown 'healthy' root. If you hold a root hair in between your fingers and you can slide the outer layer of the root away from the inner core it is a sure sign that the tree has succumbed to Phytophthora. 

What can I do?

Unfortunately Phytophthora is a widespread disease and quite hard to control. The addition of green compost into the growing media or soil can help. To our knowledge there are no chemicals available on the retail market to help control or prevent the disease. The Mycorrhizal fungus (Rootgrow) supplied with your tree also helps the root system to fight off Phytophthora but it will not prevent it.  For further information below is the Wiki link to the form of Phytophthora that Wollemi Pines suffer with: http://en.wikipedia.org/wiki/Phytophthora_cinnamomi

Alternatively the Wollemi Pine is known to coppice so if you think the top of the tree is dead or dying but the roots are OK, the best thing to do is remove the top of the tree either 3 inches above soil level or above the healthiest looking branch using sterile secateurs or a pruning saw. The tree will produce a white exudate which should seal the wound. Hopefully if the roots are still alive green buds will develop on the remaining trunk producing a bushy tree. If you want a more upright tree in the future it would be best to choose the strongest leader and remove any side shoots.