You are not alone but I am not super worried about it. I am, like you, likely to have to do a clean install soon since I will get a new computer and would like to be able to install the full version of Sonar again. If I can't becaue the servers are down I will have to go with CbB version, not what I prefer atm but I can live with it.
I don't know the ins and outs of the hosting of those auth servers but wouldn't be that hard to say something like "they will be up atleast until the end of xxx" or whatever.
The answers so far in other threads indicate to me there is no immediate shutdown planned, so that is the assumption I am going with, knowing full well things can change. And if they do, hey its not teh end of the world for me really. New version seems to work fine.