First thing my oncologist said to me some 7 years ago, "You aren't going to die"... TKI's extend NEAR normalcy (aside from costs and what can be tough side effects) to sufferers of CML.
Within a month or two of starting Gleevec or TKI your husband's blood will most probably be near normal. I get blood tests each month now (for other reasons) and NO ONE knowns or can tell I have CML from the standard WBC data. I look perfectly normal.
Exercise, as mentioned, is very helpful. I do not get tired as some seem to; My side effects are 'nausea' so I take the gleevec at night and headaches - some skin eruptions ... BUT Gleevec destroyed my testosterone production and SOME doctors still contest, so hormones might be (might) an issue to watch. Once discovered, I am nearing normal again (had gained 30 #s while dieting until discovered!). I do have bone aches, another possible side effect. BE careful not to ascribe EVERY strange thing to Gleevec, seems to warp people's outlook and bring on real depressions (for example, my aches 'can' also be attributed to injury induced arthritis so I don't completely blame the meds). As far as sleep is concerned, try to get that 7 hours nightly, body (all bodies, not just CML) need it.
While most won't, I decided (due financials) to (after these nearly 7 years) take the meds "one month on, one month off" and monitor. As Medicare does not cover the BCR tests, I do standards and have not noticed any change. YES, Trey and others will say, "Have the BCR..." and that is one of the best but Out of Pocket is approx $1K... so cannot. But you will monitor. I was MMR very quickly way back when I was draining the bank to pay and so right now, well I am just doing what I did then except every other month. There is another digital genetic test (BCR as well) that gives a very exacting read on 'how well' one is doing - being used for people GETTING off meds, so remember, some people are being 'healed' and going off TKIs, this test is not common yet)
From a perspective of 'average' issues, responses, your husband will recover, approach normalcy and live out his expected span of life. The TKIs are a miracle and, while a very small percentage of people do not respond, the average is remarkable in quality of life and length... make sure you have some 'fun', relax if possible (working all the time is not fun), be sure to try to live normally. CML is a bad illness but we now have an amazing medication that allows us to move on and remain productive. God's Blessings upon you and your husband!