abandoned?
Short answer: No.
Longer answer: I've been slowly working on it since the first release whilst encountering lots of delays. My other game, Isolation Project, came about after the PC with Return Project save data was being repaired for extended periods of time. It became a real hassle for me to transfer large amounts of data between machines each time I sent it back, especially when repair ETA's were originally promised in days, rather than the weeks and months it became.
tl;dr: Return Project will *ahem* return when Isolation Project nears its end.