Thanks for the offer, @guy038 , but it’s probably not worth the effort (I didn’t have any earth-shatteringly helpful ideas in that Topic).
It just rubbed me the wrong way that an OP can unilaterally delete an entire Topic, thereby deleting other people’s posts.
Thinking about it more, I’d probably rather have the Topic Tools > Delete Topic feature disabled completely (for non-admin users), rather than the conditional “if older than T or if other posts than OP”, because it would probably be simpler and thus more likely to be possible. But as @dail said, moderator/admins don’t have the power to configure the forum, so it would probably have to be the owner to do it (if possible at all), and I don’t know whether @donho would spend his time tweaking forum settings anymore.
Again, thanks for the input (and for letting me vent).