If someone doesn't pick up my phone call even ONCE, my mind starts immediately rushing through various scenarios in which this person might be hurt, injured, car accident, mugged, dead, etc. I worry a lot.

For the internet, if someone I talked to regularly disappeared for more than 2 weeks without any sort of notice, I'd probably assume the same things about them that I assume about a IRL person who doesn't pick up their cell. And I'll keep on assuming that they're in some sort of bad situation until they come back to say that they're alive and well. After 6 months, I'd assume that they were dead, and I would be sad.