[ravjo]

As per the article, the SpaceX vehicle due for launch later this month will only carry two of the four astronauts originally planned. The two empty seats will be used by the two delayed-return astronauts when the vehicle returns in February.

[tgsovlerkhgsel]

That's the intended return vehicle, but "lifeboat" refers to how they will get home if they suddenly need to leave the station due to an emergency now (before the SpaceX vehicle launches).

The answer is here: https://news.ycombinator.com/item?id=41470523

[nightshift1]

I don't think nasa has a concept of "lifeboat" considering there are not enough seats for everyone currently in the iss.