Hi!
Yes, if you choose that option the AI will play with the standard rules: she can get replacements on a structure without a depot.
I think using hardened attrition for the Ai also can be too big a handicap for her
About Ai destroying depots, on some previous versions of the game engine (on WIA and also on AACW and probably NCP) the Ai had the bad habit of destroying her own depots
This was supposedly fixed by Pocus on one of the latest patches.
If you see some concrete strange depot auto destruction by the AI i think it would be useful that you reported this with a save game so AGEOD could check it.
I will be on the look for this on the 1755 campaign i'm playing now
On the other side, it can be intended that an Ai garrison blow off one of her depots or forts before you take it by assault. There is an Ai rule called Scorched earth for it.
Lodilefty knows better than me how this work
But if the Ai is voluntarily destroying her own depots safe behind her lines, this is definitely a bug.
Regards!