It doesn't currently happen though, if someone lines up 2 players, then it is an automatic forfeit and the end result is automatically 25-0.
I understand your point that in reality teams wouldn't be able to not field a team week after week, but I just don't see a good way to solve this. The salary floor already means that you are wasting money if you don't meet the salary floor, so forcing people to have players might be pointless, except it makes it a bit more realistic. But is the amount of programming necessary worth it just to make it a little more real? I don't know how hard it would be to code, but if it is too hard then I think my suggestion of simply filling all empty spots with lucky fans might be easier.
Realistically I'd rather not see teams forfeiting games at all, I think it ruins the fun of it.