But I like the thought of Uncle Bob being afraid of death because he mattered, like maybe his fear was about not being able to protect John anymore.

If he can’t really actually feel it then he probably can’t actually really feel afraid. I suppose that kind of conflicts with the reason he can never cry. James Cameron's 1991 ultra-blockbuster 'Terminator 2: Judgment Day' bears some of the usual logical inconsistencies that will come baked into any time travel story, but its premise is easy enough. Sarah is about to lower Uncle Bob into the molten steel and she asks if he is afraid and he says yes. It cant be bargained with, it cant be reasoned with. There was a really good line that was taken out of this part of the film. More importantly, the terminator was saying that while he understands these emotions he can’t ever actually feel them. John changed that (along with flipping that swtich).

It has never felt what it is to be irreplaceable. It has never received love, never knows what it is to be important to someone. In other words, the terminator can be a killing machine and cause people to cry in pain and fear. When Uncle Bob was about to sacrifice himself he saw John cry, not because of physical pain but because he was going to lose someone he cares about. The terminator understands physical pain and suffering, hence his assumption that is what causes crying. There were many instances where the terminator was able to associate crying with pain and fear but John crying for him at the end was the first time anyone really directed real empathy toward him. What is interesting to me is that the Terminator (Uncle Bob) has seen all the main characters cry: John, Sarah (when she tries to kill Miles), Miles himself and his wife.

Terminator quote never stop