This is an interesting question and I think the actual outcome would be dependent on a few different scenarios.
1. Would Musing survive if Quora released it's own Crypto on Ethereum or another blockchain?
In the scenario where Quora released their own cryptocurrency on a blockchain that wasn't Steem I think then it's highly likely/guaranteed that Musing would survive, I believe currently that Musing's user base is quite different from the Quora user base. I believe both platforms would exist in the same way we see now, you would use Quora if you currently use Quora and you would use Musing if you currently use Musing. Some Musing users may go and try an earn Quora too, but I think overall a lot of users who currently use the Steem blockchain would prefer to stay using Musing.
2. Would Musing survive if Quora released an SMT?
Putting aside the massive rewrite Quora would need to do in order to work on the Steem blockchain and overall huge changes to their user experience. If Quora were to create their own SMT I believe that it would be harder to predict if Musing would survive, this is because Quora could easily become the go-to question and answer platform on the Steem blockchain overnight, their current user base is already huge and they would be able to onboard thousands of people to the Steem blockchain almost instantly. The big question would be how would Musing differentiate themselves from Quora, currently Musing doesn't show ads and everything is immutable. We would assume that Quora would do the same if they released an SMT.
I think the hard part going forward would be on-boarding new users, I believe the early adopters of Musing would stay, but I think it would be harder to onboard new users with such a big, well-established competitor. Of course, Musing may still tick along and have enough users to keep moving forward, but I believe the overall growth of the platform might be somewhat compromised in this scenario.
They would need to raise an additional round to fund the creation of all those accounts if they were to launch a SMT. LOL