How to keep on my P90X schedule?

Okay so I have had some trouble following through on the p90x schedule, as soon as I started I realized that I was going to have problems doing it all in order, I had a vacation scheduled for a month after I started and I am not able to do P90X while I'm there so I decided to extend my first three weeks to a fourth one and then take a week off then, but the few days before my week off I haven't been able to do it either thanks to unexpected occurrences and I was wondering how much this slacking will really effect me and what kind of exercising i should do while I am gone to be ready for the second series of exercises, I was thinking just normal push ups and pulls ups and running but I am worried for some reason about getting off track, could anyone give me a break down on what happens to my muscles on the off time? I would like to know whats going on with them so I can understand how to maintain good shape when I don't have the opportunity to keep schedule.