A memory leak is where a process acquires memory and then forgets about it and keeps acquiring more. This only becomes a problem when there is no more memory.
Most server based processes will acquire memory and keep it for reuse, this saves the overhead of re-acquiring the memory later. So over time a process’ memory use will increase. Hopefully to a steady state. If you have lots of available memory all the time, then you have paid for something you didn’t need.
While you may have a memory leak, I do not believe this is causing Biztalk processing to fail. You still have 1 GB of RAM available so Biztalk is not constrained by a memory shortage.
You say that the FILE adapters are failing. This is more likely to be the cause of the problem rather than a symptom. What is the error message in the event log