while some of your arguments are spot on, no, the game wouldn't have to be re-written.
granted some coding is required, and some server is needed (for the best solution), but it can be done.
and even without server, it can be done, just need that both player (in case of two wich is the least ideal case) also send their respective ship metrics at the start of the encounter, thus shall one disconnect, the remaining could still be "online" for the one remaining, with it's shield / hull etc.... since we already have those metrics..
then all whats is left is.....wait for it.....to keep sending datas to the server...like it is done now
said server having the ability to validate if they are acceptable or not (and i hope this is already the case btw, or we will have serious issues soon)
the ideal solution would be that the server itself runs the "logged off" ship, but this would cost more.
so yes, there ARE solutions, mister "I've coded software for 20+ years....."