if no one mines anymore (because there's a sudden alien attack centered right on the asics, because they built them with a material that will self-destruct on a certain date etc. etc.) the difficulty will drop drastically in a short time. at that point mining will resume Because at least I will start mining with CPU like Satoshi
If the mining hashrates dropped to the extent that people are just using CPU to mine bitcoin, the blockchain security would have reduced so much and it may harm the blockchain.
What I know is that all countries can not agree to all ban bitcoin. As one country will ban it, the other country will support it. This is according to what we have seen. Nothing will stop miners to use ASICs.