I'm not a doctor, but my two cents worth -
I do believe that most of us, pain-free or not, will eventually (if MRIs were to be made of a random sampling of the population) have abnormalities of the spine such as ddd, arthritic changes and disk bulges by the time we are in our 70s or 80s.
To answer the original question about gel though, no, from everything I've read it does not grow back. The disk gradually "degenerates". The space between vertebrae gradually narrows as part of the process of disc degeneration. Bulges/herniations/ruptures or whatever else you want to call them are part of the process of degeneration of the disk, although yes - disks can also degenerate without bulging.
Here's one study, just one example, with findings that make me write what I did above
"Abnormal magnetic-resonance scans of the lurabar spine in asymptomatic subjects. A prospective investigation.
...There was degeneration or bulging of a disc at at least one lurabar level in 35 per cent of the subjects between twenty and thirty-nine years old and in all but one of the sixty to eighty-year-old subjects..."