We get back to “context” (and the reason that we have courts and juries… and attorneys).
There was no context or setup given to the example. The driver on the wrong side of the road may have been incapacitated or the vehicle may have been partly disabled due to a mechanical problem. The driver may have been driving at a very slow speed while looking for a house number, and inattentive to his position on the road. He may have been trying to avoid a worse accident himself, such as when a child runs into traffic and he swerves to avoid striking the child, there being no time to apply the brakes and stop. That’s “context”.
If the driver in the correct lane did nothing at all to avert the accident in this case, then both will share some of the blame or fault for the collision. (A police investigation, if undertaken, would probably determine that one driver was driving “too fast for conditions”, which may even be lower than the posted or implied speed limit. Both drivers could be cited, in fact.)
“Last clear chance” is a nice legal phrase to know, but if you were the driver on the correct side of the road and were not attentive to the blockage in your own lane, and therefore did nothing to avert the accident, then you’d be at least partially to blame. In that case, you would have had a “last clear chance” to take some evasive action (or at least slow your own vehicle to mitigate the damage of a speed + speed head-on collision.
If the offending driver is simply driving willfully (or drunkenly, or asleep, or in some other careless or reckless manner) in the wrong lane and collides with a driver who does try to avert, avoid or escape the collision, then he could be found to be completely at fault.