I'd be interested to see more info from the Park Service if the shutdown happens. Word from Red Rocks NCA in Vegas is that Law Enforcement Rangers will still be on duty, and that visitors entering during a shutdown could be ticketed. That makes me think that the county providing law enforcement won't automatically ensure that people will be allowed in.
From what I have read elsewhere, visitors will be given 48 hours to vacate the National Parks following a shutdown. This implies to me that entering after that period, or even during it, could be trespassing or some other crime.
I'm sure information will be more clear following the actual start of a shutdown, though they are saying the NPS website will likely be offline.
I, too, wanted to get up to RMNP. Let's hope everything is worked out quickly!
This is the info I just pulled from CNN.com:
"All national parks would close at 12:01 a.m. on Saturday. Parks that have actual hours, like the St. Louis Arch or Washington Monument, just won't reopen. At parks where people camp, gates will be closed so no one can enter. Those in the park will be given 24 hours to leave. Parks like Yellowstone and Gettysburg, which are large and contain public roads, will be passable but all gates and visitor centers will be locked and closed. Most park employees will not report to work. Law enforcement will remain to protect parks and the public."
RMNP does have a road through, so that might remain open. But it sounds as if use of the park is not allowed.