Sometimes they do not feel any guilt about not responding, but you have to let this go. The illness can mess with a person’s mind so that the true self is not in the driver’s seat.
If you are able to reconnect, you will need to set loving, but firm boundaries in areas where you may not have before. Ex. “It’s not ok for you to be disrespectful when you speak to me. If you are experiencing difficulty with emotions, we can take a step back and work through things in a positive way.”
You need to be in a place of strength and love for yourself where you can keep those boundaries, and you may need to set them often.
When you are calm, at a level of higher consciousness (unconditional love, compassion and forgiveness), you may want to approach them, and share that you understand they may need space and that you will respect that, but equally, you value them and your relationship, being out of contact hurts you and you’d like to work together to find ways to communicate in a safe way for both of you. Then ask them what are some ways they can envision that happening and what does success look like for them.
In the mean time, work on yourself to become the best communicator you can be. Do this for you and without any expectations of it having a certain outcome.
What has helped me recently is practicing forgiveness. I hold a picture of the person who has caused harm, while sending them unconditional love. I repeat the words “I forgive you” over and over, as I send them love.