You'll all have to transfer to the same server. I don't see why it's such a huge deal tbh. Any guild that isn't dead won't have too hard a time getting their members to coordinate moving to the only available option I wouldn't think.
Not to mention if they DID try to do what you're suggesting we probably wouldn't get transfers this year.
The big deal is they don't get to chose, they don't move together. IF the destination becomes full and they swap to a new destinition and only half the guild's characters have been transfered then the other half goes somewhere else. Thus destroying their guild and making them having to wait to "pay".
Bioware is not handling this correctly everyone should be getting a free 1 time transfer with the first ROUND only being dead server mergers. This is all they've promised us..the rest is pay or leave.