brdprey, in answer to your questions, "it depends on quality of construction, type of construction and a whole host of environmental issues. You're not likely to have significant damage before the area dries out, it is possible to have damage and mold or mildew but not to likely if you take care of it ASAP.
Our prior Class A had a design and construction problem in the rear. It was virtually impossible to locate the leak, final (the rig was over 20yo) I found the problem. There was not one shred of evidence outside but the vinyl wall covering inside a series of cupboards was coming off. I did not have to reconstruct any interior or exterior walls but I did need four tubes of caulk and a whole bunch of work to fix the design error.
I have tried to stop a leak during the rain and never been successful. I try, if the leak is bad to cover the area but just to keep water away, not to repair. That I do when it's dry.
Preventive maintenance is absolutely imperative, but, it is not always the answer.
"I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to go". R. L. Stevenson
David Bishop
2002 Winnebago Adventurer 32V
2009 GMC Canyon
Roadmaster 5000
BrakeBuddy Classic II