Never messed with the tracks on a machine like yours but talking about driving a master pin with an 8 lb sledge is wishful thinking at best. The smallest sledge I've ever managed to get one out, or in, with is a 10 lb and that's a very rare occurance. More typical is the one I put back in a repaired 953 CAT's track last week. It took a 16 lb and about 30 minutes of swinging it to get that pin back in. Just glad he had broken a link, and the pin was in the replacement link, so I didn't have to drive anything out.
That said, as Pete mentioned in his reply, if it was loose enough to come off then it should be loose enough to go back on, and if you back off the idler adjustment it will be even looser. Might be a PITA to get it back on that way, and there have been times when it simply can't be done due to where it got thrown, etc, etc. However, if you can get to it easily, especially if you have another machine and set of hands to help, it'll be alot easier than trying to break it. Good luck.