While most of the Lab Rats get killed off rather unceremoniously a few get very sad death scenes.
Gia dies horrifically and screaming in the simulation but it looks like the doctors will be able to revive her on the table in reality. Instead they just draw out her suffering a bit more as too much of the simulated damage was transferred to her real body for her to survive.
Alex's death happens really quickly and suddenly but his girlfriend's reaction sells the sadness of his death despite most of the others' dislike of him.
Dana gets a Hope Spot where it looks like they're going to survive since they outlived the others, disabled their implant and a senator is shutting down Quinlan's pointless deadly project, but succumbs to the malfunctioning transponder implant that's given as the last minute explanation for why they've been seeing/hallucinating the ghosts of the other Lab Rats for the last few issues.
From the pilot, Bree, Adam and Chase never experienced a normal childhood at all before meeting Leo, they had no concept of school, friends, normal food, parties, even going to the upper parts of the house, or outside. They also never called Mr Davenport 'Dad', he treated more like employees than his children.
In Rise of the Secret Soldiers when, after a failed mission, the whole world turns against Adam, Bree and Chase. To make matters worse, an angry mob of protesters show up at their house to try and force them out. When Leo accidentally exposes his bionics to them, they drag him into the chaos, forcing Adam to blow them away with his super breath. Unfortunatly, this results in the public being afraid of Adam, Bree and Chase once again, and the team dissolving.
Bionic Action Hero was the biggest one yet; Bree arrives too late and sees that Chase died from being experimented on. Adam really lost it and wanted to end Giselle. Bree of course, almost cried, which makes it all the more heartwrenching. Sure enough, it was a fakeout, but Bree realizing she sent Chase to his death was quite a tear jerker.
"Lab Rats: On the Edge", when Leo realizes he was (accidentally) responsible for causing Taylor (formerly S-1) to go blind. What makes this tragically ironic is that she was the reason Leo got that arm in the first place. To top it off, he decides to quit the Academy and call off his own team.
Douglas' interactions with Marcus in "The Vanishing" after the latter has been brought Back from the Dead are just sad to watch; looking back, Marcus had a strained relationship with Douglas, that Doulgas hardly gave Marcus any real love, and Douglas did leave Marcus to his death, but that was then. Marcus eventually realized this, developing unending hatred because of it. Douglas, who had just accepted that he's ready to be a dad, could not bear to see one of his sons hate him so much. Douglas pleading Marcus to let go of his hatred and be a family with him again is heartwrenching in that while Douglas has changed and regrets what happened to Marcus, Marcus refused to believe that can be possible. It came to show how deeply hurt and wounded Marcus was over his father's betrayal.
On a similar note, Douglas casually stating that Marcus will “burn out” by the time he’s sixteen. For all intents and purposes Marcus is his son, and Douglas doesn’t care that he’s dying.
