i.e. I think his death was to remind her why to not travel with the Doctor. Or at least that's how I interpreted the scene, so I was always fine with it

Especially since his death was Martha's fault in the first place. It may have been a reminder of all those who had suffered for her in the series 3 finale

I feel that Martha suffered so much during the season 3 finale, walking the world, watching people die whilst hunted by the Toclafane. Also her family being held hostage/tortured by the Master. I always interpreted Peck's death as a reminder of the horrors of travelling with the Doctor.