This is not quite true - I use T1 drones extensively in mining missions. It takes discipline to ensure T1 drones always have a place to unload, but accomplish this and missions are reliable and completable.
It used to be that the site respawned the next day. That as unmade in an update more than 6 months ago. Any loss (including theft from another player) and there is no way to replace the missing ore. (Stockpiles from previous failed missions excepting and excepting blackmail/extortion payments to other players for extra ore). The only recourse then is to beg favors from a GM for a mission reset.