Personal Injury Settlements- Broken Wrist with 3 surgeries

I was injured as a passenger in a car accident. The other driver (who was at fault) only gave us $25,000 because that is the maximum coverage his insurance had. The car I was driving in had only liability car insurance.

My hospital bills 2 yrs after the accident and 3 surgeries later are:

1st surgery $21,000, plate and 8 screws wrist fracture
2nd surgery $7,600 to remove plate(1 year after accident)
3rd surgery $13,700

One of my nerves was completely cut and my left wrist will be numb permanently.

There were 2 more incisions made at my 3rd surgery to severe additional nerves. Cortizone shots and pain management added to $5,000.

physical therapy and chiropractor $3,000.

So about $50,000 in medical bills, and since i just had the 3rd surgery 1 week ago, I don't know how bad this will affect me.

My personal injury attorney received letter from car I was driving in ins. to settle for the $100,000 liability, and to leave the under-insured $100,000 open. PIP paid $30,000 of medical.

Since we have signature from the claims adjuster stating that if we settle for $100,000 liability insurance,with the condition that under-insured claim stays open,

What are our chances and when can we file for the under-insured. Also how do they calculate pain and suffering?