No quibbling from me about whatever shortcomings there might have been with Peter Mansbridge. Overall, he has always been a consummate professional .  The National has always been the best TV newscast in North America ( and also the UK from what I have seen) in terms of presentation and reporting.  
However Mansbridge's retirement is likely the end of an era. The major evening  news format has become outdated. No-one wants to wait for a set time each day to find out from one figurehead person what is going on at home and around the world. The 24/7 News channels are much more relevant to people now.  So kudo's to the CBC for looking at a different way of delivering the daily news. I hope that includes seeing the CBC break more stories that matter to all Canadians.. The taxpayers deserve it.  Right now it seems like the Globe and Mail is doing most of the work in that department. 
Enjoy your retirement Peter! You deserve it. You have served all of us very well.