We can only give our own opinions as there are no set answers on all that and with that is also the confusion of people with ME and CFS being used interchangably.
I'll express my opinion on your questions but Im refering to the ME subgroup of CFS if people want to call it that, which meets the international ME guidelines or the canadian consenus criteria and not refering to the CFS patients who may just have fatigue and depression or a missed other illness.
-Do you think there are stages in the development of CFS?
yes. Dr Cheney which I classify as a ME expert as he was one of two main dr involved in the Lake Tahoe ME outbreak. He has described very well the progression of my ME when he talks of the stages of it. Actually I've seen him put it in more then just 3 stages with the order things in body usually go down in. I cant find the link of what he's said but this one summarizes it describes it
http://forums.phoenixrising.me/index.php?threads/stages-of-cfs-development.43540/
-If yes, what are these stages, and what could be the timeline?
I think Dr Cheney has a got a time line in the info of what he said, I'll have another look after I post this for the article.
I myself have also noticed a bit of time line in many ME/CFS patients eg those who die from this (not counting suicide or accidental ODs or accidents).. Ive noticed that these ones generally have it long term.. eg over 8-9 years. Ive personally noticed that more die from it around the 12-15 year mark of it. The more severe you have it with the more systems affected, from my observation the more likely you will die from it. In my own case, I truely do believe its going to kill me directly or indirectly.
Is CFS mandatory becoming worse in time or could it become better in time? Or just could stagnate?
Some very lucky ME ones do have a remission (something which Dr Cheney has spoken about sometimes happening in first few years), thing is they will always be suspectable to getting this illness back with another trigger. In my case I had a 2-3 year remission but the caught a virus going around which everyone was getting and ended up back with ME.
So some lucky ones do fully recover and may even be lucky enough to stay recovered if they arent triggered back into this by say a vaccination, surgery, an illness or another event well known for triggering off ME. (full recovery not all that common though most never get back to how they were before the illness, one study showed full recovery to be as low as only a few percent).
A ME person could have .. a progressive illness, one which improves and they could recover.. or it could stay at a certain level of illness so they could be sick but stable. There is no rules. I guess it all depends on what the person is doing and what complications with the illness the person carries.
Is CFS without any treatment a deadly disease in a time window of N years ? If yes, what is N (i.e number of years after one patient of CFS without any treatment dies)? Or is it a disabling disease one can struggle and live a wretched life for 50 - 60 years ?
It wont kill most, for most it will leave them suffering a severe disabling disease or leave the person at a lower level of activity then to which they had before getting it. Most dont have any true treatment other then trying to treat symptoms as there is nothing currently offically recognised in treating ME patients.
Are there cases of patients of CFS known to have lived over 40 years with CFS? Are there cases of patients of CFS that died of CFS?
Ive known people who have been sick for over 40 years..but Ive only even known 2-3 who have had it that long out of all the 100s of people Ive got to know with this. Generally those ones who have had it that long havent had it as severely as I have it (by this I mean with as many complications) though they still are quite disabled and be unable to work so yes one can have it that long. I think it probably actually kills the severe group before that long but that is my own personal view of things.
Anyway, do remember for most that this illness will not kill them so if you or a friend has it, dont worry about dying from this unless you obviously have a progressive ME or severe with lots of complications. ME people have suddenly died from unexpected complications even when they appear to have been doing better but its not worth worrying about as most will not.
In my case Ive developed due to this 2 leaky heart values I must have one of those holes opening in my heart which many ME patients get), very unstable BP to the point its dangerous.. (can spike over 190 in 1 min of standing or my dystolic can ditch to 20 or lower) and are starting to get organ damage from this illness
eg one blood test showed that my kidneys were struggling and hospital dr said Im at risk of kidney damage ( due to the dehydration this illness gives me), eyes - a scan showed optic disk swelling probably cause the high BP spikes it causes due to its made my autonomic system unstable etc etc. Two out of the 3 people I met who's BP was doing what mine does they both went on to develop actual heart failure. They were not old. I now have an epi-pen as I started to develop severe allergy reactions etc etc.
So many different things with this illness could end up killing me. I developed asthma with it too and cant take the drugs due to my MCS (chemical sensitivity) to keep things like my very high cholesterol level in check so further putting me at risk.
If a cure isnt found, I do think I will be dead from this illness before Im 55 years old my complications get worst with time with the way my life is currently (so I see myself having less then 10 years left to live. With ME Im living with a life threatening illness. . Ive got ME 17-18 years ago... 2-3years of that time though was in remission)