The Forrestal class can (and did) fly off anything in todays carrier airgroup inventory.
The ships were decomissioned because they were old, not small. The ships major components become more and more expensive to maintain, especially when parts have to be custom made for the old (out of production) systems. I’m talking boilers, water evaporators, catapults, elevators, and so on.
Eventually, a major rebuild becomes more necessary, and with more frequency. Example: A propeller shaft or two loosens up, a “wobble” developes, and that shaft(s) has to be shut down. (And ship’s top speed and cruiseing endurance drastically effected. Until it is fixed, more stress is placed on the remaining shafts.) To fix it, the shaft has to be removed, the seals and bearings replaced, and a new shaft (remember, the old one sagged and got bent) put in. That’s a major dry dock operation.
A further consideration is this: The Washington Naval Treaty of 1922 put serious brakes on Capital ship construction. Great Britain had the largest (and constructurally, the oldest) fleet in the world at the time. As she was not allowed to replace the older ships (except for adding the HMS Rodney and HMS Nelson) for some time, no new battleships were laid down until 1935 for the HMS Ark Royal (a carrier) and 1937 (King George V class Battleship). One of the main problems preventing Britains rebuilding their fleet (when they realised Hitler might be a problem) was that the military ship building industry was allowed to whither.
The US might be hoping to avoid a similar problem by continually ensuring that some construction is always ongoing for CVN’s, subs, and surface combatants. Therefore, as a new ship (like the USS Ronald Reagan CVN-76) becomes available, you retire some older ship (like the USS Constellation CV-64), as an increase in overall manning levels have not been provided or authorised.
For the topic at hand, the US could reactivate and rebuild the mothballed ships (like the aforementioned Constellation). In a long war of attrition, this might be necessary. But reactivating these ships would probably take at least a year, probably two. The cost in money would be high, but if the need was dire enough, then the cost would have to be born…
Caveat: The longer a hull lies in a mothballed state, the more work has to be done to refurbish it, and make it suitable for active duty use. The ships decommissioned in the 90’s can be brought back online relatively painlessly, but something a tad older (decommissioned in the 70’s) is gonna be problematic, IMO.
As far as manning levels go, the Navy has a large reserve: http://www.navy.mil/navydata/navy_legacy.asp?id=146
Which will tide them over until draftees come online. It was the policy in WW2 to “seed” experienced active duty and reservist personnel into newly commissioned commands in an attempt to mitigate the “newb” factor of the new recruits. It was largely successful.