"Your PhD advisor isn't going to hold you after your cancer diagnosis" — not saying this would never happen, but it's certainly not the norm. "Together till death do us part" (as, sadly, was the case here) is, however, common.

It sounds like you're taking about "that world" while not being a part of it, or having a clue about how things work there.

Mentorship is a relationship, and the relationship with one's advisor isn't just lifelong — it's enshrined in history forever.

Look up the math genealogy project. I can track my academic lineage hundreds of years back simply by going up the chain of who-was-whose-student.