I made a topic before discussing this bug when it happened (and redownloaded 0.7) but, this time when it occurred (when I was building a set and just had one animation part done) I decided to close the box showing the error. However all my Mineimator added items/objects/characters etc. remained in the same position with the same characteristics as I had edited them.
Not losing all hope I looked at the scenery and bob's your uncle there was no schematic loaded! So I just loaded the schematic that I had imported via the world importer (which thankfully saves the schematic) and everything was back to normal.
So if you run into this bug/glitch even now or the future, see if closing the error box allows your entities to remain and reload the schematic