So ultimately, do you actually have a problem with rendering the square the character starts in as no longer threatened ... or the chance that this will give anyone -- PC or enemy -- to avoid AoOs?
No, of course, not. It's just the mechanics of withdraw as the RAW says that I have a problem with. There should definitely be some form of withdraw.
What about the restricted withdraw? Would it suffice as your game's "standard" withdraw action?
(quoted from SRD)
Restricted Withdraw If you are limited to taking only a standard action each round you can withdraw as a standard action. In this case, you may move up to your speed (rather than up to double your speed).
Wow, I haven't seen that (or rather I probably did and forgot about it). No, for me, all you could do is step to avoid an AoO. Like regular withdraw, I believe the move action only allows you to move, not to parry as you move.
I'm still pondering over using my original 2e house rule: you can withdraw up to half your move as a move action (essentially rewriting parts of the 5 ft. step). In the restricted withdraw, you could use the single action to withdraw up to half your movement. In the end, I'll probably allow a step as the only way to avoid AoO.