This is something our office regularly does especially on drawings where there's a ton of information. We separate our drawings so that we can delegate areas so that two or more people can work on a given site. what I like to do is insert xrefs as overlays so that I can see where my partners have left off or working on, and we regularly save; then we get notifications, and we reload drawings. I also create a master base file that has both mines and my partner(s) irrigation base to be later converted into blocks then exploded to tie the two (or more) together. this works especially great if I'm working remotely and my partner is in the office. When all is done, we'll go back to the master base file, convert to block, explode, connect & size mainline.