Yes, Thompsontown is still surviving. As far as Lewistown being open on Columbus Day, I doubt that any government offices will be open but possibly the McCoy House and the library. What, if anything, might you be looking for?

The Mifflin County Historical Society and the McCoy House Museum have web sites. My schedule of events for the his.soc. shows it to be open on Tuesday, but not on Monday generally. I woud suggest that if you are traveling a distance you contact them by telephone and inquire if some very nice volunteer would meet you on Monday since you are coming from out of town. The volunteers were very helpful this summer when I went there, going out of their way to help me find things, made copies for me, etc. To me it was well worth the annual fee to belong to the society and to receive their newsletter which is full of history, etc. The Genealogy Nut