I'm so sorry about your friend's husband. My DS's dad has just died from this in the past week
so quite raw for me but I can offer a few pointers perhaps from a place of grief but also insight:
It did feel unreal in the beginning and I desperately wished we had done more things then while we could - travel, eating lots and lots of delicious food he loved, adventures and memories and recording his voice and generally just making videos and safeguarding memories for my son.
What happened for DS's dad is that although it was starting to get painful to eat before treatment started and he was a bit scared by that, the treatment itself wrecked him (to be fair he did have both chemo and radiation at once, no surgery) and it took him ages and ages to get over the effects of the treatment. He had about 4-6 weeks of feeling normal over christmas, and then it returned and he went downhill so fast it was heartbreaking. There was no time for beach trips then, he felt too tired. He was in pain and taking pain meds which made him woolly headed and then the pain weirdly went away a week before his death, then he started coughing up blood, had a few major haemorrhages and sadly, a final catastrophic bleed which killed him. No-one thought he'd die so fast, he felt he had months or at the very least weeks left. It was and is still so upsetting.
I don't want to be the voice of doom but - tell your friend to grab those precious memories NOW. Say all the things they want to say to each other - don't leave anything unsaid. Reminisce together. Thank each other for the time they shared. Get his affairs in order, make a will and pre-pay a funeral and then hope for the best, he may be one of the lucky ones. But if it doesn't work out, they will have cherished each moment while he was still relatively well and they will have fewer regrets if he does eventually pass away. I can't stress enough how much I wish I'd known how short time was. We had no idea really and it was a terrible shock.
He was only 62. I was telling him to go to the doctors from Jan or Feb last year, and I think it was already pretty established at that point. He finally went to his GP in March, started treatment in July 2021 and has just died this May, 2022. It's a hard thing to go through, your friend will need all the support around her she can muster - and she's lucky to have you as a friend. 