Although it's not great, having to wait half an hour for the next bus when you've arrived a minute before it leaves isn't the worst thing ever. When leaving events you should expect to have some wait for a bus home. It would often take you just as long to get your car out of a giant parking garage.
It is, however, a perception thing and how people behave is not necessarily predictable based on the "logic" of people on these boards. After all, participation in discussion about things like transit and urbanism on a board like UT already, I would suggest, makes the people on here far more likely to accept those situations.
The reality though, when you mix in those "regular folks" who are not on UT is far from that. As people have pointed out, the ACC might well be one of the most transit accessible arenas in North America. Yet the road congestion before and after a game/event is markedly different than on non-event nights. The conclusion is obvious, even with an arena attached to a subway and regional train station and right across the street from a regional bus network a significant majority of people still choose to drive.
The follow on conclusion, then, has to be (in my mind) that an arena in Markham with far less transit accesiblity will be even more car centric. That is not, in and of itself, a "bad" thing as long as it is recognized and plans are made for that. What scares me is when, for whatever reason, the plans are made assuming there will be a higher than likely transit usage. I think this will be very car centric and I would rather that was recognized and planned for (in terms of road access and parking) than not.
If the Stouffville line can do three runs back to the city after events, that would be about 6,000 people that could be accommodated right there within an hour or an hour and a half-ish. As someone mentioned above, if there are bars and restaurants nearby, people can just grab a beer and take a later train.
Four pretty major assumptions there:
1. Off peak, southbound service is available with 12 car trains.
2. 6,000 people (30% of arena capacity) will be heading in that one direction
3. 100% of the 30% will be interested in transit
4. 67% of the 30% (4,000 people) will be willing to wait around for between 60 - 90 minutes.
I love that this arena is going up....I love that I don't pay taxes to the municpality borrowing the money to build it....I accept that if I attend events there, I will be driving.