Oh goodness, I'm so sorry to hear about the missing voice microphone icon from your keyboard. Good thing this VZW detective is on the case and ready to crack it. With that said, let's take a look.
First off, kudos on everything you've done thus far. Your troubleshooting tactics have been extremely in depth and perfect for the situation. The other thing I would try here is clearing out information about the messaging application. Simply go to settings > application manager > all > messaging > clear data and force stop. Then power cycle your phone and retest. Please keep us updated how this works as we may need to go further. Regardless, we'll get you set back up.
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I had the same problem, missing microphone while trying to voice type a text message.
I found out that I needed to enable/ update the app "Google Search."
Go the the Play Store and search for "Google Search" and enable/ update it.
Then, go to your language and input settings to make sure "Google Voice Typing" is checked and the settings are how you would like.
Hopefully that will work for you too.
Son of a ......... That did it! I do remember disabling that bar back when I got my phone because it took up real estate and I didn't see a need for it! Who in the world knew that it was tied to the microphone!!!
Wow... thank you! Microphone is back and I don't think I'll forget how to fix this problem....!