After stroke recovery concern. Concerns?

One fine morning, my father couldn’t walk properly, and there was a change in his face and speech. We rushed him to the hospital and got him admitted. The doctor assessed his condition and started medication along with tests like X-ray, MRI, etc. The next morning, while still in the hospital, he couldn’t get out of bed or walk. The right side of his body became completely numb, so we rushed him to a multi-specialty hospital. He was under observation for 3 to 4 days. After this, he recovered within 1 to 2 months. Now, he can ride a bike and walk properly, but the flexibility and strength on his right side are not as before. He was diagnosed with diabetes when he was around 42 years old and was managing it with tablets. After this stroke, he has been taking insulin injections (20 units in the morning and at night) along with BP tablets for the last three years. My concern is: Are there any side effects of insulin? Can he switch back to tablets? And are there any other concerns?