I think it's almost tautological. But most people are on a spectrum, there are extremely nihilistic people who still care about their mothers for example. But yea, I think that the spectrum of nihilism is just the inverse of the spectrum of willingness to live.
> presupposing that a life of suffering should be ended
I'm not prescribing action, I just think it usually ends up this way.
> An example of a line of thinking you might accept; a nihilist could decide go on living, just because they feel like it.
I believe many people live like this, but not because they are a nihilist, but because they don't do introspection and/or take meaningful things in life for granted, because just a tiny bit of introspection would reveal that there are many many things you find meaningful in life, even if its something basic like, security, health, or peace. If you take these things away from a person, they will probably contemplate their existence and try to figure out why they should go on with life.