It is often said that the Black Death ended feudalism in Europe by driving up wages. Is this accurate? Was feudalism still an institution in most of Europe at the time of the plague?

Ultimately there is a lot of debate around whether or not feudalism is a useful concept for describing the relationships between rulers and their vassals/the governed in medieval Europe. This debate is also not particularly helped by the fact that everybody has different ideas about what feudalism actually was; some historians describe it as only being the system where a King or Emperor gave land to his vassals who swore to serve him and others choose to include serfdom and the manorial system as another aspect.

Nitpicking over teminology aside, I'd like to quote an answer I gave to a similar question about the Black Death and its effect on the institutions of Medieval Europe.

We don't have enough data to precisely calculate the numbers of dead, but estimates range from 30% to 60% of the entire population of Europe and as many as 175 million people in total. To put that into contrast, that's the same as the ten most populous states in the USA being completely wiped out by disease. The church was particularly badly affected, as priests who gave last rites to the dying and the monks and nuns who cared for the sick had a high risk of catching the disease.

The immediate consequences of the Black Death were wage rises, better social mobility and more freedom of movement for rural workers. There was more land per farmer, so individual farmers became richer and the price of food went down. There was also less focus on agriculture and more on livestock farming due to the lack of workers to harvest grain and so more meat, cheese and milk became available. Landowners also offered higher wages due to a critical lack of labour, so rural workers were able to find jobs further afield, leading to a further decline of the manor system where rural workers were in effect bound to the land. Eastern Europe was less heavily hit by the plague due to a more spread out population so these effects were not as pronounced and serfdom continued in these countries for a while after the west.

Due to the concentration of population, towns were worst hit by the plague and many large cities and settlements lost up to 80% of their population. The city of Bristol was said to have been left so deserted that grass grew several inches high between the cobblestones in the streets. This led to an even more pronounced rise in wages and skilled workers and craftsmen could command high prices for their work. There were however attempts to control this such as the English Ordinance of Labourers in 1349 which attempted to restrict wages to their pre-plague level and to control the movement of workers between employers. A similar ordinance was issued two years later to reinforce the original.

Ultimately the Black Death led to more freedom for rural and urban labourers and a decline in the power of the aristocracy. The Church was also badly affected and lost much of its local influence due to the death of many clergy and monks.

It would be fair to say that the Black Death was a significant factor in the end of Serfdom in Western Europe. However, the institutions of feudalism, such as the aristocracy survived, and in places less badly hit by the Black Death such as Eastern Europe, there was no material improvement in the lives of the everyday worker.

With regards to the second half of your question, most European states were under what could be described as a feudal system in 1345~ with the notable exceptions of the Byzantine Empire, Italian Merchant Republics and City States and the Emirate of Grenada, in that they had a more or less absolute monarch and a system of vassals, but the vagueness of the term feudalism really precludes definitive categorisation.

Marc Bloch's 'Feudal Society' is a good starting point for reading about Feudalism whereas Elizabeth A R Brown's article 'The Tyranny of a Construct: Feudalism and Historians of Medieval Europe' is the definitive counter-argument against Feudalism. The BBC 4 In Our Time Episode on the Black Death is a good discussion of the events themselves.