Stopping the leak is the important first step, but delamination usually occurs only after the underlying wood and framework have become saturated with moisture. Even after stopping the leak, the wood can stay wet due to the absence of airflow and further damage could result. Some people proclaim you can inject glue behind the delamination and stick it back down. Typically this is a waste of time and effort, as you cannot get glue to stick to old adhesive and wet wood for very long no matter what you use. Also there is no opportunity to repair any underlying damage or even time to dry the wood effectively.
If delamination occurs and the area of the damage is small compared to the size of that section, a good body expert can repair the damage with a patch. In your case of delamination on the front of a RV, I would recommend replacing the entire front, as it is a relatively small area and the cost to replace vs. repair (if the damaged area is small) is insignificant, especially when you consider the integrity of the repair. Replacing the entire front is guaranteed to be a more robust repair than a patch. A patch is also not an option if the damaged region spans a significant area. The repair process involves stripping the moldings and other fixtures, and removing the fiberglass panel from the wood frame. The insulation is removed in order to dry the wood frame and interior wall panel. This drying stage is very important for proper repair. Any water damaged wood framing is replaced, new insulation installed, and the wall material replaced with new, including any backing that was used on the original.
In the case of a patch, it is done the same way, except only the damaged portion of the fiberglass is simply cut out. Then the framing is dried, repaired and a new section of fiberglass is inserted into the cutout and the joints finished with fiberglass cloth and painted. This is a relatively complex repair job and I don’t recommend you attempt it yourself. Seek out an RV repair facility experienced in collision repairs. The job should not be overly cost prohibitive, since a front wall is not a large area to repair, however, such things are subjective!