I would think that over time the flexing of the cable retainer would not be a "good thing" for the remaining bolt.
You might take a piece of wire or an icepick and see if it is a blind hole or if it goes all the way through. If you can determine the depth of the hole and compare it to the length of the bolt, you may find there are some more threads in the hole and a carefully installed, slightly longer bolt, may hold until you have a reason to take the side cover off and fix it properly.
If you end up putting the original bolt back in for show and leak prevention purposes only, a judicious smearing of RTV on the threads may help hold it in place and seal it up temporarily.
Judicious Smearing - that'd be a good name for a band....!
