I can guarantee you all one thing - because of the way the ticketing system works with FCB, you will always find a ticket on the official website. Irrespective of what game it is, there is always tickets that suddenly start showing up on the official FCB website. You're talking about a stadium of 100k people, it's basically impossible that every ticket is sold out. What happens is, most members who are unsure / don't care that much tend to give their tickets to friends and family, and if they aren't doing any of that, they open it up for sale.
However
,, a disproportionate number of people open up their tickets one day before / on the day of the game. Whether it's the clasico, the United quarter final, Tottenham, Lyon, etc. Each and every game, my friends were able to easily find tickets all of a sudden, at the last moment. The exact same thing will happen for Liverpool too, only problem is, people naturally get nervous and assume they aren't going to get tickets, and end up overpaying third party's for them.
My suggestion to those who want to fly down, I'd say do it. If you don't get tickets on the official website, getting tickets from third party's isn't that hard, you can always find someone who knows someone (For example, I know quite a few tickets being sold by my friends in school right now, legacy carnet holders).
Good luck to those looking for tickets, and hope to see you guys at the Camp!