It took me about 12 attempts over a few weeks to sign up. It always got stuck at the "submit" and would just load endlessly, but never send the confirmation mail.
Different computers and phones and browsers and happened across multiple servers. ...I can totally see how that drives away a lot of people.
I think reddit will eventually shrug it off. There's an enormous number of users who think their app is perfectly fine and claim to not even notice the ad spam. Whether they're blind or braindead is another question and I don't get it, but most people don't care.
The ones who do care are the ones who still know old.reddit and make the platform worthwhile with their expertise. As those people migrate elsewhere reddit will become even more mediocre and irrelevant.
Reddit will survive, just like Twitter and yahoo are still alive. But eventually nobody will even notice that it's still alive.
At some point it'll be easier for Google to buy reddit for the content than to unfuck their own search engine. Bonus points because they can tell themselves they fixed it for good and keep making google search even shittier.