Honestly, I done listen to any of those bands. I never got into them. There are few songs that I like and thats it. We cant argue with other people taste in music. I was never into thrash/heavy metal.
At the moment there are many good metal bands from all geners. Many will become well know, not world wide but in metal comunity.
Will there ever be full stadions or arenas? I doubt it. Not in our generation (beside bands you have name above. Iron maiden, slayer, metallica etc). Will metal/rock become underground scene? Yes, you can say it almost is.
But heck, if people prefer pop/rnb/rap over metal/rock i could really care less. I know what I like and i will listen to that.
Metal/rock will never die, maybe they will become underground but there will always be bands and people who will love and live for that genre and will support their favorite bands no matter what. I know I will.