Zodiac - the signing periods in NBA and Europe are after the signing window in NBL so basically Vasiljevic secured an NBL contract for the next 2-3 years for I believe a far better coin than he was on and will try to lock in a deal in Europe or NBA later. From what I'm hearing there is a genuine interest in Europe but whether it will happen that's a different story. Indeed the money is better in Europe, but players on many occasions don't get paid or get cut without payout so not all rosy.
Most leagues in Europe are about to finish in 2 weeks and then teams will start finalizing the rosters, which should happen by the end of June, rarely goes into July. As Mystro said, the clause is likely valid till then and then he gets locked in as far as Europe is concerned. As for the NBA, the summer league starts early July with camps sometime in September, so I'd think the NBA clause will remain open as long as it's practical. From a marketing point, it is always in the NBL and club's interest to have a player picked by a major league.
Watched him play at DV yesterday and the Kings should take a chance and play him as a point from time to time, with his drives he kept collapsing the defense leaving his teammates wide open. If they converted a half of those looks, he'd have more than 10 assists. Apparently had 8 a night before...
Good luck to him, whatever he decides to do, won't hurt to play another year for Sydney...