"... if Bitcoin drops below $1,000, mining now becomes unprofitable... ." Wrong! If Bitcoin drops below $1000, what will the miners do? They will stop mining, or at least slow down their efforts, due to no profit. Then, what will the Bitcoin algorithm do if the correct number of bitcoins is not being mined daily? The algorithm will become easier, so that it will become profitable for the miners to start mining again, even though the price falls well under $1000. Then the miners will start mining again, and things will go on just like before.

There are only a few things that can stop Bitcoin: 1) Internet or power grid crashes; 2) a method of cracking the encryption is found/developed; 3) People are intimidated by their Government to give Bitcoin up; 4)governments and banks make a significantly and recognizably better altcoin.

My knowledge of bitcoin may be imperfect, but I was led to believe that the act of "mining" was actually crowdsourced computation that served to bookkeep other people's transactions in the global blockchain, and the "mined coins" were actually a commission for performing the bookkeeping computations required to maintain the bitcoin system. Is that not true?

The Bitcoin blockchain is an encrypted "ledger" of Bitcoin transactions. It is almost 170 gigabytes in size. Thousands (Millions?) of people have downloaded it to their personal computers. The encryption is such that if any one blockchain on any one computer is tampered with, or is otherwise corrupted, it will be rejected by the group in consensus fashion. Miner creations of new bitcoins is built into the Bitcoin-core located at https://bitcoin.org/en/download. The mining, itself, is separate from the blockchain until a new block has been mined, which then becomes part of the blockchain. Anybody who has Core on his computer can mine for new blocks. Because of big miners and ASICs, mining with a regular computer is impractical.