He absolutely will not be forgotten. He is a hero. Even now he has a wikipedia article, multiple movies about him, tons of support from the people supporting the freedom of information and those who are sick of the secretive bullshit going on behind the curtains.
one man's hero is another man's villain.
And in either case, when they are relevant enough, they are not forgotten.
But do you honestly believe he will be relevant enough in 10 years?
No doubt some will remember him, but I say way more people will know Snowden than Assange in ten years.
He was well known 10 years ago and he is well known today. By extrapolation, it is natural to assume that he'll be also in 10 years.
The founder of wiki leaks forgotten in ten years?
With all due respect but the chances of that happening are quite slim.. Julian Assange will end up in multiple history books whether you like it or not.