Can I rescue a batch that may not have had enough water at its start?

Adding water will lower your gravity through dilution. It will also dilute out all your other attributes (flavor, alcohol, mouthfeel, color etc etc).

Being stuck at 1.058 seems too high to be simply off due to water dilution (unless you forgot to add several gallons to a concentrated boil). Being stuck at 1.058 is likely a fermentation/yeast management issue.

Without know your recipe and process (and actual OG) its hard to offer solutions. However you may need to think about making a larger active starter of fresh yeast and adding that. Hopefully you have enough volume in your fermentor to do this. Another option would be to just patiently let this beer sit. Brew another beer and rack directly on the cake of that beer after it finishes out. Again this is all BS and speculation without knowing your recipe and process from brew day.

Not sure what yeast you used but assuming it was a Belgian strain which are more tolerant to higher alcohol levels, then I would certainly look at pitching rate like the last answer said. If the yeast was pitched right out of the fridge (cold) you might have shocked the yeast, or if the yeast got to hot before pitched same problem unhealthy yeast pretty much going to die. you can also stress the yeast out by simply under pitching, I always make a starter no matter what style i brew but it is a must for brewing big beers. there are about 100 billion yeast cells in both white labs vials and smack packs, I do a 1/2 cup light DME to 1 liter water starter and that about doubles the yeast cells in 24 hours, I would suggest using a pitching rate calculator to determine how many cells you need per beer then create a starter accordingly. reading back through your question it sounds more like you might have to many unfermentables, in this case you could brew another batch with a higher attenuating yeast and less unfermentables and blend the two together! just be clean