In RL, injuries can help ruin a team's season (Texas) or not (Purdue, Syracuse). In RL, it comes down to depth (or consistent recruiting success, if you prefer) and to a coach's ability to adapt.
I see no reason that including a semi-random feature that does the same thing for HD coaches should be removed. If I were to have my best player go down for the year, rather than complain about it being out of my control, I would just go about adjusting my depth charts/game plans to give my team the best chance of winning.
I would say, though, that regarding firings there out to be a protection for coaches who experience injuries. For example, if a team lost X number of player-games to injury in a given season, that coach cannot be fired, regardless of record.