I am not telling you what you should or should not do. I am posing a question. If you get a heart attack and refuse medical care for example I don't consider that suicide, you will die as a result of your inaction but you did not initiate your death, it was not your intenr or premeditation that caused it.
As far as chasing immortality, assuming you had any say in it, any means of staying alive is natural unless you are talking about supernatural things.
Given that many conditions are irreparable, the general direction of the logic that we always want to live if enough things could be changed (i.e. so we enjoy life) is a truism that doesn't mean anything. Even if all forms of dementia get cures, they won't be restorative for those with it today.. for example.