Based on my experience living in Christchurch and having read of the Westpac stadium's preparedness for earthquakes, I'm thinking the stadium will be okay.
You can never be 100% certain until a proper engineering inspection is done but the strength of the earthquake as it impacted Wellington in terms of significant factors like ground acceleration etc. was much less than experienced in Canterbury in February 2011 - you were a long way from the epicentre of Sunday midnight's quake in Wellington. We were much closer in Christchurch and the Sunday midnight quake was not strong enough to cause any significant damage here.
I'd think that the stadium should be built (and the ground beneath it prepared) to withstand much larger impact quakes.
A really major damaging quake is quite a different thing to what you experienced in Wellington this week.
Christchurch was closer to the epicentre of this one but the energy got directed north towards Wellington because it occurred in the same tectonic plate we are on. Christchurch is on the other side of the plate boundary. The shaking here was stronger - not anywhere near as strong as the Christchurch quake was there but still strong enough to damage modern buildings and cause liquefaction around the port, which is where the stadium is.
Edit: here's a map of the shaking intensity which shows how it was worse in Wellington than Christchurch despite being further away