A simple solution is to make mining prospect missions point to comets (gas) and asteroid fields (minerals) without a sun, so they don't go nova. :-)
that would require the creation of new object classes etc for the game ... and probably new properties to be set for all star / planet objects so others cant accidentally find the comet etc for the missions
without access to the guts of the game to scope it out my suggestion when an error occurs (star is nova) ....
is they turn into 'return to earth' missions in the cargo bay ?
or that they become PoW (instead of passenger) cargoes ?