He had a shot at becoming head of the party with the most seats. As such he would have been asked to form a government. That would have been a win. As it is now people are saying he really won because his party picked up seats. Well the Democrats picked up seats last November. That didn't make them winners.
He would not have formed a government. Every single party has announced that they would not participate with him in forming a coalition government. His win would have been significant as a demonstration that the Dutch people have had enough and demand change, and that might have had an impact on whatever government eventually was formed but he wouldn't have formed a government. The other parties hate him at least as much as the democrats hate Trump.
First, the Democrats did not pick up seats last November. Second, even if Wilders had controlled 40% of the seats, which was the highest pre-election prognostication I have seen, that would still have left him unable to form a coalition government as all the opposition parties announced pre-election that they would not support Wilders to form a government. No one expected him to take power. This was a victory, but the war continues.