Did the first chapter state that the saints die in the first place?
It mentioned that "its been some time" and that the miasma built up quite a bit, but the mention of "in the end" doesn't explicitly mean "before they died" (else the god would be wise to immediately summon another one).
I personally believe (with no hard evidence) that they stay until the miasma is reduced to "safe" levels, and "in the end, before they return, it takes about a year to gather the miasma up."
I think it is purposely being misleading, but is actually much kinder than it sounds.