I confess to not being aware of last week's cme size and type.. so probably should defer to a better informed reader... but in the meantime..
NASA did have a set of protocols for making the decisions that might be required (I've got a link here somewhere...(see below)), from simply re-orienting the spacecraft to put most of it between the astronauts and the problem, through to a complete mission abort to bring them home to safety and/or treatment.
The decision would be made not only on the amount of radiation, but also its type, speed and direction, the likelihood of it being a one off event as these often are, even whether there was any reasonable chance of avoiding it, and how far thru the mission it was. Bear in mind that back in the 60's, things were a bit more 'pioneering', you might say, so I suspect that if it was borderline they may have erred towards mission completion rather than a small risk of long-term effects to the astronauts (being expendable test-pilots and all...
Also, these events are exceptionally rare and the craft were quite well shielded, so the chances of one affecting a mission were close to vanishingly small. Compared to the other risks inherent in a mission like that, it was almost a no-brainer.
If it had happened during an Apollo mission, would it have been a show stopper?
I doubt the CME alone would have done much harm to a crew in the CM or two astronauts bunkering in the LM on the surface of the moon. I wouldn't have liked to have been an astronaut on the surface of the moon if a large CME occurred, but this is mainly because of charging effects.
CMEs and flares are very different. CMEs actually occur several times a day during the solar maximum, and are due to large rearrangement of the magnetic fields in the solar corona. The average speed of CMEs increases during the solar cycle maximum, travelling faster than the solar wind on average. This drives a shock through the wind. CMEs take anywhere between 2 and 6 days to reach Earth, and the particles are relatively low energy.
Hoax proponents like to use them as another example of the terrible radiation that permeates space, describing huge storms in the Earth's atmosphere produced by killer CMEs. To be quite honest, most hoax proponents don't even know what one is.
The reality is : CMEs produce millions of tonnes of protons and electrons. Fire this into a magnetic field and it will change the shape of the magnetic field. Take the particles away from the magnetic field and it will snap back. This is what happens at the Earth. The CME 'squashes' the Earth's magnetic field on the day side, and causes it to tail out into space on the night side. When the magnetic field lines on the night side reconnect, the magnetic energy stored is released, and it radiates back to Earth.
So, the huge storms that the conspiracy theorists like to quote aren't storms of deadly particle radiation, but rather electromagnetic storms.
However, back to the question. Very large CMEs can drive very extreme solar proton events (SPEs), the sort that can produce protons with energies above 100 MeV. These SPEs are rare though, and occur maybe once in a solar cycle. In fact, looking through the literature today, it is now believed that CMEs are responsible for extreme SPEs. These are the SPEs that hoax proponents like to sell as typical, when in fact they are very infrequent.
This scenario is exactly what occurred during the 2003 Halloween storm. There was a large CME, and it drove an X class flare, which produced some fairly energetic protons.
So, if there was a warning of a massive CME prior to launch, it might have stopped the show; partly because of the risk of large SPE, and partly because of the potential impact on communications between Earth and the Apollo craft.
Had the CME occurred after the launch, the CME itself would not have been a problem from a health physics view. If it had been accompanied by a large, but rare SPE, then that would have been different, and potentially quite harmful to the astronauts. However, before I get quoted out of context, the SPE I am talking about did not occur during the Apollo missions. I'm talking about the sort of events that produce very high fluxes of 104 cm-2 s-1 at E > 10 MeV, and occur maybe once per solar cycle.