I think their solution to that is to replace all of the parts every 4 years.
At that point you can just let it sit there "forever" if you want. Not that you would of course, you'd want to clean it up.
If the drain between the core and the drain tank fails AND the both other passive cooling methods fail to keep the core cool enough then yes eventually the core vessel will fail. In that case, the fuel escapes the first containment (the primary loop) into the can. The can drains to the fuel drain tank so we still provide cooling.
The alternative is a Fukushima-style transition from "working reactor" to "unapproachable death trap generating clouds of hydrogen gas which can explode the containment dome, sending toxic radioactive smoke from uranium fires into the atmosphere (while other material leaches into the ocean via the water table)". Even Fukishima's spent-fuel cooling ponds required water be added for for weeks and weeks on end.
If you'd like it to keep the reactor working while walking away from it, that's another matter which is keyworded something like "unattended operation" not "walk-away safe".