Arnold

I have to get an honest realist opinion on this situation. The inground liner pool is over 20 years old. So is the liner. It's 30 foot 3-10 foot deep. It belongs to my elderly parents. The pump is disconnected since last fall. We are in the northeast US. Stretch tarp cover in good shape. They can not care for it and funding is an issue. What would happen if it was just left alone? What is the minimum that needs to be done?