We will all die of something, Demonslayer. Physical death is caused by the body failing in some way. Your mother in law did not die because God did not love her enough. That's just the way her body stopped working. Bitterness at this isn't going to help you, or your wife....nor would it have helped your mother in law.
And yeah, the above statement sounds pretty heartless, I suppose, except for one thing. I have Multiple Myeloma, which is cancer of the bone marrow and it is not curable. period--unless one has an identical twin with healthy bone marrow. I don't.
Unless I get hit by a semi in the morning, that IS how I'm going to die, and while it won't be within the next few months...or even, if all goes very well, within the next couple of years, that's how I'm going to go.
"Faith,' in a lot of ways, is THE most mis-defined word there is. Almost everybody I talk to uses 'faith' and 'belief' interchangeably, but they are not. The bible talks about the difference between the two concepts...I don't know whether the Quran does or any other religious text. Belief...is belief. "Faith," is the trust it takes to actually act upon that belief. You know...'works,' as in 'faith without works is dead," and "even the devils believe, and tremble.." In other words, a closer synonym to 'faith' would be 'trust,' rather than 'belief.' Faith is what you DO about that belief.
....and if something wonderful happens, and one beats cancer, and one wishes to give the glory to God, what's the problem with that? I mean, if He would cure ME, it would be a verifiable miracle, but hey; I"m OK with it whatever.