questions

does this happen or does durability drop only when attacking? If durability goes downhill when being attacked, I can see this as a perfect tactic to ruin someones bot(s) while he/she is offline ^^

It drops during the course of the fight, but returns to what it was when the fight was initiated, once the fight is over (for the defender, or person being attacked).

that way offline people can't get trashed by being attacked a million times until all their armors are broken and they have to camp everything again :(

Slight correction. Condition drops during battles, not durability. Condition is what affects weapon damage, armor defense, and shield block. For attackers, durability is used to restore condition. For defenders, condition is restored automatically.