like Agemegos says, if you can't hear, then everybody needs to use the text chat window. If the other players just talk using the webcam, you'll miss what they are saying.
As other say, gaming and chatting in the text chat works just fine, and is how folks have been doing it prior to tools like Roll20 or Skype for decades.
I would say, that there is the makings of a new suggestion for Roll20 in this. Pipe the audio into a speech to text tool so what people say turns into text in the chat window.
According to a conversation I had with an interview candidate today (he works at a dictation software company), Windows 7 actually has a built-in utility for this that apparently doesn't suck. My own clients use DragonDictation (the MD version).
Just saying, that it is not impossible to solve this problem for a deaf person while still allowing the other players to talk.
Heck, getting a chat log of the verbal conversations would actually be pretty cool. It might also rein in some of the out-of character banter because players could directly see that what they say is getting logged and disrupting the narrative text.