Here's an interesting question in a highly unlikely case Austria were to be annexed to Germany: would Austria become a land, or each of Austrian lands would separately gain the status?
Austria would become the 17th state of course. It's very unlikely that the 9 different states would become individual German states, making it 25 states.
Also, the re-organisation mentioned by tack50 and True Federalist is unlikely, because citizens of the 9 Austrian states are very associated with their own states and do not like these states to be abolished or merged with other states. For example, I as a Salzburg resident would not like to be merged with Carinthia. I cannot say why exactly, but it is like that. I assume many people from Virginia would also object to being merged with West Virginia ...
All of this assumes a democratic scenario of a merger with Germany, assuming that the population of Austria and its states have a say about what to do in terms of re-organisation.
If there was a dictatorial takeover, none of this would matter anyway - as Germany would re-organise Austria and its territory as they wish (like the Nazis).