What happens if a memory pool is deleted while there are still open handles to that memory pool? Or what happens to the memory behind the pointers that are still held?

All the resources including memory allocation gets automatically freed up when the process gets deleted. Also, all memory gets freed up when the pool goes away. If applications still use the memory pointers then we will have unpredictable results (seg faults are typical). Since OS Abstractor actually tracks the amount of memory allocated and available, it is easy to check its control block for memory leaks in application prior to actually deleting these pools.