I can't imagine why someone would jump to the conclusion that someone is being disrespectful for using the image. Especially if they've been using that avatar for years. It's not like it's a satirical image of Gary. Gary himself voiced it. I doubt he took offense at people using it as their avatar. (I don't want to speak on behalf of him. That is not my intention.)
Personally, if people were using an avatar of me while I was alive, I wouldn't want them to stop when I've passed on. Doing so serves no purpose.