The question is not can you make a game using only open source. That is a definite yes. What you really want is to be as productive as you are now. You probably won't be. It will take some time to master the new tools. I think the new tools can be as effective but that will take time. If you have problems with a tool like LibreOffice, file a bug. Open source developers may not know about the problem you have. I use LibreOffice for work all the time. My colleagues do not but they can read my files without any problem.
Good point, productivity. In the case of game develop, as I learn so far, without good productivity, is simply not possible, that's why I used this word. It's different from editing text with Libre Office, is possible as long I spent hours in communities discussing workarounds (I had to use a xml editor to manually edit the file). The bugs I saw are already listed, and I had contact with people involved, so I hope the next versions will come fixed - it's my office now. We must think about tools that if not perfect (is there such thing?), is stable, nice to work and have a good community to deal with bugs, though.