question

It's been said before, it can happen but is extremely unlikely. I don't mean to be too offensive, but unless you're SERIOUSLY weird, like cape wearing weird or you talked endlessly about your collection of porcelain dolls, or you dont have a questionable reputation or absolutely horrible grades, you probably won't get dropped By everyone.
Fairly certain like maybe 10 to 15 girls TOPS got completely cut from all the chapters. Out of 1345 girls, I think you'll be fine.

It happens. The girls you talked to in the past 2 rounds might have liked you, but it doesn't mean that the girls that talked to you during philanthropy round will like you and you can be dropped. Just because you get invited to philanthropy round does not guarantee you an invite to preference round, just like being invited to preference round does not guarantee you a bid to that sorority

It's really hard to get dropped from EVERY sorority. Like you have to seriously have a personality defect or have horrible GPA or something like that. You might get dropped from a group you really liked (or all the groups you really liked), but really, if you learn to focus on who has been inviting you back and not the ones you got dropped from but really wanted, then I think you will see the chapters that are inviting you back see something in you that they like and can see you being a part of their sisterhood and maybe you will be able to see yourself there too.