Is the F-117 fleet at Tonopah Test Range being mothballed?
Some F-117s under storage (not in active service) were still flying sometime back because their storage type required for it. Attributed to USAF by http://intercepts.defensenews.com/2014/11/we-now-know-why-the-f-117-is-still-flying/:


  Per Congressional direction within the FY07 National Defense Authorization Act the aircraft were placed in Type 1000, flyable storage for potential recall to future service.  In order to confirm the effectiveness of the flyable storage program, some F-117 aircraft are occasionally flown.


The same article gives some details about the type 1000 storage: 


  Aircraft in Type 1000 storage are to be maintained until recalled to active service, should the need arise. Type 1000 aircraft are termed inviolate; meaning they have a high potential to return to flying status and no parts may be removed from them. These aircraft are ‘re-preserved’ every four years.


However, this may soon change as the House Armed Services Committee’s version of the National Defense Authorization Act repeals the 2007 provision for storage:


  This section would amend section 136 of the John Warner National Defense 
  Authorization Act for Fiscal Year 2007 (Public Law 109-364) by striking subsection (b), which would remove the requirement that certain F-117 aircraft be maintained in a condition that would allow recall of those aircraft to future service.  


So, while F-117s are not in USAF service, some were still flying (until recently) though they are probably going away for good soon.