Though you provide all the information you have, it is difficult to know exactly what was happening, how the treatment helped or did not, and if there was more that could have been done (this is probably behind why you are asking). We as pet lovers do the best we can for our guinea pigs.
I don't know what signs of illness you saw the week before. If there was bloat, this is very serious, causes pain, and can interfere with eating. Not eating has its own problems and can contribute to malocclusion. We recommend weighing at least weekly and daily if illness is suspected. And being an observant owner. Hand feeding is vital (provided there is no blockage - the blockage, we don't know when it started and what caused it).
In some cases, seeing a vet within hours is required. In other cases, perhaps a few days. I think it depends on condition and the precise problem the guinea pig is experiencing.
Read this carefully:
It helps to have a skilled and experienced vet.
Sometimes a necropsy will provide additional information and help you understand what happened.
That night I watched him at feeding time and he did seem interested he would snuffle in and around food but just wouldn't eat, he would occasionally pick something up in his mouth then drop it out again. The very few times I did see him eat it looked like he had something stuck in the side of his mouth as he would open his mouth to one side, if that makes sense? This is why I thought maybe he had something wrong with his teeth. -the vet actually said his teeth weren't too bad, however this is once they had anaesthetised him and had a really good look!
I didn't notice any bloat, however I've not seen it before. And Murle has always been a big boy so maybe he was but I just didn't realise. I know for a longtime he could never tolerate being sat upright for cutting his nails for example, maybe this position put pressure on his stomach? Also he suffered with impaction which we helped him out with regularly.
What is a necropsy? Like an autopsy for guinea pigs?