Hi Koncho.
1 I stopped taking the tablets 8 months ago, but in the current state no-one will say I am fully cured. I have a blood test every 2 months. Even those who have been off the tablets for 2-3 years still have blood tests every 3 or 4 months. The term used for those who are OK for a sustained period without taking the pills is treatment free remission (TFR).
2 Everyone is different on side effects. Some people have very little; some people have side effects so tough that they have to change medicine. For me, I had bone pain for the first 2-3 months, but all the 10 years I was on 400mg, I had flatulence, occasional nausea, occasional fatigue, and cramp after I exercised. These were much reduced when I went down to 200mg dose for a year before I stopped the pills last October.
3 The best advice for your father is to make sure he takes his pills every day. THIS IS REALLY IMPORTANT. 1 week is quite quick to see a change in blood results, but there should be significant change inside a month. If WBC is very high some doctors prescribe other drugs to help reduce that.
It would help the forum help you if you can share some of his results, particularly WBC. Also if you have results for a FISH test or a BCR/ABL test (it might be called a PCR test) let us know that. These are the important results against which progress is measured. FISH is the most useful test early on to understand the extent of the disease. When FISH results get very low, BCR/ABL is a more complex test which can measure lower amounts of abnormal cells, which is typically more useful 6 or so months into treatment.
A couple of other questions. How old is your dad, where is he being treated and was it picked by chance or was he ill when diagnosed? All these will give people on here the best chance of helping you through this.
I will add one more comment - largely to save SCUBA from having to type it. It is very unlikely that CML will be the cause of your father's death; if he had to get a cancer, this is a better one to get than many.