There don't seem to be any restrictions on Hapsburg troops moving back to either one of their capitals from anywhere on the map. Just want to confirm that I'm not missing anything as I have troops in France that I'd like to get back to Vienna. Thanks in advance.
If you are removing units because you no longer have political control of those spaces(either because you are suing France for peace or because France sued you and bought fortified spaces back for VPs or cards) then you can either go to
1. The nearest fortified space
2. Either Capital
However, you don't get to move troops out of a space if you are retaining political control of that space.
Unless there's some errata of the 2010 Rules I'm missing, Paul's answer is incorrect. There is no attrition during the Suing for Peace segment.