Whether they get a full rollback in salaries or not, if they put in a hard cap or some other salary structure, at a minimum, they need to rollback how the present salaries count against the cap.
The negotiation, IMO, really comes down to this:
Is David Stern and the NBA full of crap when they say they're losing 350 million a season or are they actually taking such losses? As I've noted, Forbes details on the franchises show a considerably higher operating income than that.
If the franchises are losing as much money as Stern says in reality rather than due to accounting tricks then the owners will play hard ball with the players, and the owners will win. The players have a remarkably short shelf life in terms of years they can earn in the league, and probably 25% of the players would need to declare bankrtupcy after a single canceled season.
Decertification could be a tremendous hammer to use against the league, but the players don't really want to decertify as it hurts more players than it helps, and there would be huge money spent on the anti-trust suit which isn't guaranteed to be successful. Both sides have a lot to lose in this scenario, as a work stoppage would shrink the pie by so much that either side is better off taking less up front to avoid a stoppage.
At the same time if the average franchise is losing 10 million a year, a work stoppage isn't really costing the many of the owners anything. They're losing money by playing the season anyway, and while they need to still pay some lease agreements/staff even during a lockout, the fact that they save on player expenses means that they'll probably be in a near break even situation whether they play or not.
As such, many owners will have nearly infinite patience in watching this thing play out. They need a new agreement to get profitability. While it will be a tough sell, the real solution to this problem is probably greater revenue sharing between the haves and have nots. No other solution is ever going to create a system where New York and L.A. can have a salary cap that fits their revenue at the same time the Memphis Grizzlies have one that fits theirs.
Can the owners negotiate that amongst themselves? There are many sides that need to come together, and few of them are looking out for what's best in the league. The haves and have nots on both the owner and player side have significantly different views and motivations then their peers which explains why these negotiations are always difficult.