What would you do?

I've got an idea for a military addon aircraft. I've been using this particular configuration for a couple of months, now, and I'd like to share it.
I've tried to contact 3 authors of existing addons to get their permission to use portions of their creations, and I can't seem to get a reply. I obviously don't want to use anybody's stuff without their consent, because at least one author explicitly asks not to. Cool. I respect his wishes.
But, what do you do if an author doesn't reply, for whatever reason? (I know, don't use it.)
Does there ever come a point where, after reasonable attempts to contact a person, where it just doesn't matter, any more?

I've tried to contact 3 authors of existing addons to get their permission to use portions of their creations, and I can't seem to get a reply. I obviously don't want to use anybody's stuff without their consent, because at least one author explicitly asks not to. Cool. I respect his wishes.
But, what do you do if an author doesn't reply, for whatever reason? (I know, don't use it.)
Does there ever come a point where, after reasonable attempts to contact a person, where it just doesn't matter, any more?
