They've stated many times that won't happen. Guilds will NOT be split up. It's a non-issue.
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.