Although I would prefer that FireWire remain an option -- for all the commonly cited reasons (such as maintaining the capability to connect FireWire hard drives and FireWire-based camcorders), the complete demise of FireWire now appears inevitable. It absence from Apple's MacBooks is just the harbinger of what's coming down the road. So we might as well start getting used to it.
If a MacBook is your second Mac, and your main Mac still has FireWire, this should be a relatively easy transition. Even if a new MacBook will be your only Mac, odds are that you've never used FireWire and will not even be aware that the port no longer exists.
In other words, this ought not to be a big deal.
Except there is one big deal here and it is a critical one for me: Target Disk Mode. As a troubleshooter, I am loathe to give up on this feature. If your Mac crashes at startup, the ability to use Target Disk Mode to connect it as an external drive to another Mac (assuming you have a second Mac available, of course) is the simplest and fastest way to potentially repair the drive or at least recover data from it. It is also the best way to transfer large amounts of data from one Mac to another.
If Apple could deliver an alternative to FireWire Target Disk Mode (allowing the mode to work via USB or Ethernet, if that's possible), I would not think twice about getting a MacBook sans FireWire. Without such an alternative, I won't be buying one, at least not until I have no other choice.
Otherwise, I note that Apple has flip-flopped on FireWire before (omitting the FireWire 800 port on MacBook Pros and then returning it in the next update). Perhaps Apple will do a similar reversal with FireWire on the new MacBooks. I doubt it. But I can hope.