Should not regret. As you, the author tried the best.

My co-worker's father regret he didn't do the 手术 for his wife who died after 4 months...

My mother-in-law, 88 years old, she wants to do 手术, but the doctor said "No" due to her age and condition of 淋巴转移... She is doing 化疗 now...

So, no regret for whatever you did... Just remember "Did you try your best to support..."