If I had my BTC in a multibit HD wallet prior to the fork, and I exported my wallet to Electrum after the fork, will the BCH still be tied to the multibit HD wallet?
And if so, how can I access the BCH stored in the multibit HD wallet?
Here is what you need to do. Make sure you have the seed from multibit.
If you have exported your Multibit HD wallet into Electrum, then your Electrum wallet is sharing the Private Keys with your Multibit wallet. In a less technical language: You have one account (your wallet) and 2 interfaces to access your funds (Multibit and Electrum).
The BCH are tied to your account not the interface. So forget about Multibit and redeem your bitcoin cash with the help of Electrum. Follow the official Electrum Recommendation on how to redeem Bitcoin Cash. Short version below:
If you do not have your seed, extracting your bitcoin cash without your wallet words works, but requires knowing how to edit and compile java code: https://bitcoin.stackexchange.com/a/51297/64842
Because installing maven, java, modifying and compiling the JAR, and using the private keys is a bit beyond most non-developers, I've created a comprehensive guide, along with a pre-built JAR file to walk you through it:
The summary is: