I guess I'm looking at the survivability. if all of a sudden something happened where majority of these ASICS got shut down (within 2-3 days, 80% of ASICs are taken offline) for whatever reason. What is going to happen? will the 20% of the ASICs left from rest of the world, going to handle the hashrate?
What's going to happen is that finding blocks is going to slow down for a while, and then go back to normal once difficulty adjusts to the lower hashrate.
I guess I wonder if one day, something happened... could ones like me who can't afford an antminer S17 get an opportunity to start hashing to keep btc alive?
With a normal PC, with about 20% of the current ASICs still alive and kicking? I don't think so (well you can, but you'll lose money), but I'm no expert in the field. You might be able to find more knowledgeable people on the subject in the mining subforum.