Who has kept gains after being off for > 1 YEAR

[James Bond]

can u loose ur gains over the course of time even if you keep proper diet and training?

Definitely yes IMO, you will lose not a small part or your gains anyway, even with proper pct and good diet and training.
While on you're more focused, strong, your body is processing nutrients in a much better way, everything is boosted.
When you come off the magic status ends and something is gonna go away, sad to say but true.

[Bruce willis]

i mean youll still retain the look and size of the muscle mass after the water loss, but u wont be as strong.