Most of the questions you ask are not answerable without context, and are more or less moot given management has already made the choice for you... unless you are asking 'should I quit and find a new job in the face of all this change?'
If your going to tough it out I recommend you read this this post on the topic: How To Survive a Ground-Up Rewrite Without Losing Your Sanity.
I recently started down the path of rewriting a bit of server logic in node.js. The main reason was it is currently written in .NET and we are wanting to migrate away from MS environments down the track.
My experiences so far have been positive, you will have an initial learning curve with all the non-blocking-ness of it but once you get past that it's actually quite fun to code in.. I know, FUN!
For one thing you have consider is that a fatal error will bring down the whole app due to it's non threaded nature, so the stakes are a little higher and you have to explicitly check and catch everything.
For those who have done both front and back - and enjoy both - not having to switch mental contexts from front end to back end languages is a real bonus that I think will ultimately boost productivity in our team down the track.