as far as i am aware this cannot be done
instead why dont you split your mission up into mini missions and have like a series that you can play one after another. Also a multiplayer map of this magnitude would certainly wreck a servers community, no player is going to hang around that long for a game to finish, or even see it through to the end.
You would have to somehow pass all the locations, damage, of all the objects, all the weapons status etc to an outside folder where the mission on reloading would then look at this folder which would setdammage, setpos all the objects. Even somebody nifty with html coding would have a nightmare creating something and probably would need something already installed in the hardcoding of OFP to be able to do it.
I would forget it mate, its way too much hassle