What medications your dad is taking? He needs to take regualr medication and follow checkups. Diabetes though cannot be cured, it can be controlled by regular and appropriate medication, diet changes and exercises. If his sugar levels are more than 250, then he should be rushed to ER to control it. Sugar levels crosing 300 can lead to other complication leading to infections, amputations and sometimes even death. I am not trying to scare you, I am only letting you know what can go worse such that you can take care of your dad well.