Well it depends on a lot of factors

It's not the number of days but what you get into them.

What sort of cancer does he have and how fit is he apart from the cancer.

There are many different cancers many different chemotherapies and people have very very different experiences.

My wife was diagnosed with peritoneal cancer in 2012, she had massive fluid build ups that were getting into her lung and needed a number of emergency drains to get her stable enough so she could start chemo. That stopped the fluid that would otherwise have killed her in short order. After her first chemo we looked at each other and said "Was that it?" mostly she got some mild flu-like syptoms 48 hours or so after for about a couple of days. occasionally a bit of bone pain and pins and needles but over a 3 week cycle that was a small price to pay - it bought her 3 years, she died in October and in that time we did so much not least we managed a 2 weeks exotic holiday.

For her that optoin was a no-brainer

Other people are less lucky and have needed more toxic chemicals or have a bad reaction and are very sick indeed -occasionally people even die from the complications of chemo.

We did get to the point where the only standard treatment had a 15% chance of working and was very toxic - our oncologist, lovely man, looked at haer and said "It's up to you but I wouldn't"

So in his position I would have a straight talkwith the oncologist and ask how bad the side effects usually are for someone in his position - I'd be asking how many side effect free days people normally get in each cycle and typically how much time it normally buys. Are we talking 6 weeks? 6 months? 2-3 years? (like my wife had)

Then he'll be in a position to make a decision

And yes your lives will be on hold and yes it will be tough - particularly at the end - trust me I know 

Put your energies into making the time he has left as good as it can be and his end as painless and as easy as possible - check out what the options are for hospices particularly if he's not that fit.

Talk to McMillan (www.mcmillan.org.uk) they can probably help with all sorts of tings like that