So luckily we found what the cause of the severe memory issues was last Friday. It turns out that it was to do with the Astar Pathfinding package that we were using. Honestly speaking it was my own fault: we had hypothesised that increase the area of the grid graph, which is used to control the pathing for some of the creatures, wouldn't impact the performance of the game.
We naively theorized that next to the graphics, the information stored would be negligible without actually looking deeper into how it worked.
The dev lead decided to fix a major section of the sewer section, and that threw us. The game started crashing to desktop horribly, and we thought it had something to do with the new sewer changes. We rolled back the change but this didn't do anything.
We looked through the other things that had changed and realized that Astar was one of them.
I incrementally took everything out, and found that by decreasing the Astar area, that the game crashed less. Eventually I decreased the size of the grid graph so that it was back to the original size. At that point the game NEVER crashed again.
We must have been operating on the brink of failure the whole time and had no idea whatsoever.
By the time I had figured it out, it had been a panic stricken 2 days where I was at the verge of giving up on the whole thing.
Fortunately that got sorted out and I could get back to marketing. A slow trickle of responses started coming back - people actually wanted to play our game!
That gave me a huge sense of relief after several days of silence. Granted, most of them were low tier youtubers, but it was a start. There were a couple of mid tier guys at 100k subs, and one guy who was 2M that responded, but we really needed 1 or 2 super high profile ones to give us that momentum for day one.
It was looking good, but we needed more. Fortunately the technical side was stabilized, and looking really good actually! I had taken a 'break' this weekend to tweak and fix things which is what I enjoy most. By the end of the weekend, I felt the game was actually pretty fun! The polish was there too - I'd even addressed a lot of the little niggling remaining issues all by myself!
So from here on in, I will need to focus hardcore on marketing and PR. It will still be a hard stretch to the finish line, but at least half the battle (i.e. the technical) is now resolved!