To automate the fetch of the insurance plan on the health services form I proposed to update the on_change_patient function and add an on_change_insurance_holder. I think it will be a time saving for the end-user.
At the most cases the patient record has a current insurance field, once you select the patient on the health services the insurance holder will be selected like the party of the patient (like it currently does) plus it will select and fill the patient current insurance as the insurance plan field.
If the insurance holder is not the party of the patient, then it will blank the insurance plan field.
It could be something like this: