If you really need things to arrive, you'd be sending them on more than one connection. Of course, the difficulty with redundant fiber connections is that really the only way to determine if redundant fiber connections are in the same bundle is with a backhoe.
If you have multiple, let's expand out to 3 instances (not necessary, but helps illustrate some of the issues better). A tells B something 10x. A also tells C something 10x. Even assuming you don't get inconsistent responses (i.e., B has both accepted and rejected the write), what happens if B accepts it, and C rejects it? Likewise, if you have high load, you're going to have race conditions leading to lack of consistency as well (A tells B and C x = 2, meanwhile C tells A and B that x = 3). You are favoring availability > consistency.