I work on Gang Garrison 2, a game still actively developed which is also reliant on a dead game creation tool (Game Maker 8.0), so this is sadly familiar.
Unity is closed-source; I'll bet in ten years we'll see the same thing happening again, with people trying desperately to find some way to run these old games that were developed on the no-longer-supported Unity platform.
http://community.clickteam.com/threads/34059-MMF-1-5-to-MMF2...