Even if they were 'locked' into the shares, they could have always collared them as Mark Cuban did (he was stuck in his Yahoo position when the market imploded, but was protected via the collar he set up with Goldman Sachs to limit the downside).
In many public companies, employees (even rank and file) are prohibitted from shorting or buying puts on their shares.
Some companies even prohibit selling covered calls, regardless of strike price. (A deep enough in the money call behaves somewhat like a put.)
I'm a little surprised that Cuban would be locked out of selling the shares but able to enter into the collar. I'm sure it was legit (since it's well known), but still...
http://investmentxyz.blogspot.com/2006/05/cubans-collar-anat...