The old blockchain will continue to exist and accept transactions, although it may be incompatible with newer Bitcoin clients. A soft fork is a change to the Bitcoin protocol where only previously valid blocks/transactions become invalid. Since old nodes will recognize new blocks as valid, a soft fork is compatible with previous versions. Only a majority of miners updating to apply the new rules is required for such a fork. Some examples of well-known cryptocurrencies that have undergone hard forks include the Bitcoin hard fork, which resulted in the creation of Bitcoin Cash, and the Ethereum hard fork, which led to the emergence of Ethereum Classic. Bitcoin Cash itself was further hard forked with the introduction of Bitcoin SV. More details about the differences between Bitcoin, Bitcoin Cash, and Bitcoin SV can be found here: <a href="https://cryptorobotics.co/bitcoin/">https://cryptorobotics.co/bitcoin/</a>.