Pausing my Sphinx entries for a moment to respond to an interesting comment by Neubert on Minion House Rules, suggesting that minions should get a saving throw to avoid being killed. Since I'm now extending the suggestions in that post, I thought I'd write a new entry that extends the earlier post.
Giving minions a saving throw against automatic attacks only is a very reasonable idea. I'll consider it option E. In terms of underlying game design, it is essentially the same as option D, in that it gives automatic damage a roll to destroy the minion, just like any other damage. The only difference is that the roll is completely fixed, rather than being an attack vs. defense roll. The big advantage over option D is that it doesn't require stretching D&D to invent rules about making attack rolls in situations where characters aren't making direct attacks. That is a very nice property. The disadvantage compared to methods B-D is that the roll has nothing to do with the amount of damage, the skill of the attack, or the defenses of the minion. Overall, though, a good option.
Giving all minions a saving throw wouldn't really address the issue of automatic damage very well, as it wouldn't change the fact that it was much more effective than a normal attack. This would be a rule with a different purpose, to make all minions harder to kill while still leaving them stateless. I've considered and analyzed rules of this sort in the past, for other purposes. This is in general a very workable rule for making things tough but stateless, though not without disadvantages. It could be used as a way to make a specific minion tougher. If you apply it to all minions, it certainly does make them more dangerous. But unfortunately it magnifies the underlying problem. Trying to kill minions with normal attacks would become so difficult as to be totally impractical; you would have no choice but to abuse your minion-killing powers to the maximum extent in order to get rid of them.