Until some one sits down and runs the numbers nobody will know.
How would an engineer go about determining whether the structure was safe, following the application of an unknown load? I can see how you can do this for an Airbus which has all kinds of accelerometers and stress-meters built in, but short of finding the van again and recreating the accident, I don't see how you're going to get the numbers to plug into the analysis. Perhaps light aircraft should start carrying some of these monitors (complexity, groan...) as they could probably be made quite light and cheap nowadays.
In hang-gliding we always used to inspect the spars for wrinkles or dents following a 'whack' or crash, and that was about it. Hang-gliders are abused substantially yet structural failure is very rare.
For this accident, I find it interesting that the pilot didn't seem to notice it. At the end of the day, if you push against a wingtip you have a huge amount of leverage and if the wing rode over the van without causing the pilot to require substantial amounts of differential brake, I can't imagine the forces were terribly large?
Even if the pilot did require substantial brake, there would be a limit on how much force he could apply through the wheel, which I guess could provide some measure of the force on the wingtip. Perhaps I'm answering my own question..?