Well although my brother's tumour couldnt be removed because of where it is, there are 1000s of people who have tumours removed and make a full recoveries.
It is hard to say too much because it completely depends on where the tumour is, how big it is etc..but with the technology they have these days, you will be surprised what they do.
My brother went to the brain unit in Fazakerly in Liverpool, they inserted a radioactive chip into the tumour, left it in for a month then took it back out. The tumour shrank and has never grown since.
So all the best for your brother in law, but as I said, they do amazing things these days!