I'd just like to address that your scenario seems pretty paranoid, and I get that due to recent school shootings, you're within the realms of reason to think it over, but otherwise...I've never lived in the US, but it's not a war zone where such things would happen that frequently.
Anyway, of course, in a reductionist sense, yes I would be glad. I'd be alive. However, it still wouldn't address the fact that a) a shooter was present meaning that a person had access to firearms and would have been able to kill loads of people with not much stopping them and that b) it is easy enough to acquire firearms that two people within about 100 could have access to deadly weaponry.
If anything, it'd make me more concerned. Yes, people were saved but at the same time, it can give people the wrong idea and may telegraph that they should always be on the lookout for shooters(which is paranoid at best) and that it is okay to break a law of this sort under "certain conditions". This could lead people to allow for more lax gun control because they feel the need to protect themselves.
At the same time though, it could swing the other way and prevent people from protecting themselves with unnecessarily strict self-defense weaponry laws(that sort of shit happens in the UK all the time). Ideally there shouldn't even be such a situation and the bottleneck is the University security.