What if bitcoin stays low like this forever and never goes back to ATH?

In my opinion you have to look at bitcoin as any investment. You should really only expect to gain 5-10% a year.
When bitcoin bubbles and shoots really high, that is when you sell.
There are too many bitcoins available and the market is too liquid to support ATH's long term. They will eventually fall back down to a sustainable level.
Following bitcion from $10 in 2013, it should really have only grown to about $20 at this point. Being that it has grown faster because of all the media from the $1000 bubble, you have to factor in accelerated growth. That is why I value bitcoins somewhere between $20-$100.