I definitely think you can revive old fanfictions. I have an old one that I wrote in seventh grade that's pretty shitty and I'm slowly rewriting it. It's actually here on Mibba. It's called Cry for the Moon.
I agree with Grump Bunny. My story, Fading Lights is an old rewrite of an anime fanfic I posted on FF.Net years ago and I'm now rewriting the whole thing to elaborate on some plot points that were overlooked. :) SO, anything can be saved.
Of course you can. I had an old fanfiction that I wrote when I was 16, it was terrible, cliche, and rushed. But I rewrote everything, and it turned out really well and people really liked it. Anything can be saved if you actually love it.