In this day and age of Google, and the Bible available on numerous websites with some pretty nice search engines, memorizing the Bible isn't quite as important as it used to be.
Christians memorized great amounts of the Bible (and for some sects, other scripture) so they could answer questions about their religion while doing their missionary work. Some of course take it too far and fail to learn the reasoning behind why a scripture is there in the first place or the story behind it, and become little more than parrots, quoting scripture but without meaning. These can easily be trapped in discussions when a topic ranges outside of and event the Bible directly discusses.
Others didn't have the incentive or the need to memorize so much of it, and it takes a lot of work and effort to memorize the thing. Understanding the gist of the stories in there is often enough, however, but they can get easily trapped in a discussion.
Trying to measure the effectiveness of a Christian by how much scripture he has memorized is at best a non-sequitur. It's not misplaced to read and even memorize the Bible, unless you lose the meaning of what you are memorizing. It's not insufficient to not memorize the Bible, because one can still refer to it quite effectively using the numerous search engines out there for it. Many of these even run on phones, making the Bible most convenient for anyone with a phone.
It is important to remember that the Bible is only a testament of Jesus Christ and God. It is not a god in and of itself, as some treat it to be. Neither is it a legal document, and one shouldn't expect every i to be dotted and every T to be crossed.
Could a Christian get by without ever reading biblical text? Is the Bible really necessary? It would seem that there exist Christians who simply don't find the Bible useful. Of course, there are Christians who are practically glued to theirs, but what if they were deprived of any Bibles for whatever reason? What would change and more importantly, to what extent would they become unable to be Christians (re: how is the Bible necessary).
The base question which could be applied across all beliefs is "Is a book/manifesto necessary for personal faith?" Perhaps it's necessary to maintain an organized religion but I'm curious as to where that line, if any, resides. Of course religions existed among illiterate peoples. Afghanistan and Pakistan are top examples of places with very high illiteracy and very high degrees of religious fanaticism, i.e. many of them are not reading the Q'ran, and in fact, in that part of the world it is illegal to publish the Q'ran in any language other than Arabic (Allah's language) which they don't speak.
Despite the Bible being accessible to all on the internet, there are more Christian denominations and sects than ever before. If the Bible were the driver of the faith then one would surmise that all the denominations would gradually merge towards convergence. Again, despite the internet ensuring everyone has the Bible, divergence seems to nonetheless be accelerating (full disclosure, I have no data handy and it is not my intention to imply that Christianity is Global Warming).
To most, it is necessary, for it describes Christ and his teachings. How can one worship Christ if one has never heard of Him?
That said, if one had lived during the time of Christ, personally met Him, and believed His message, then no bible would be necessary. Similarly, if such a man were to pass his testament down through the ages, there will be people that will still believe in Christ and His teachings.
If ten men had this experience, then ten witnesses might pass down their testimony in this way. How many met Christ and believed in His message? We don't know. But there is this to consider:
If a few of them wrote down their experiences instead of passing them merely verbally, wouldn't the result be similar to what we call the New Testament today?
Now we can take it to Karl Marx. He traveled widely, pressing his message wherever he could. Eventually, it was written down. Is this not scripture for those that believe in the message of Karl Marx? How well would he have been known today if it wasn't for that scripture?
It could be argued just the same whether we even need a written history or not. Is a written history necessary?
I know Christians who memorize large amounts of the Bible. Are their efforts misplaced?
I know Christians who have, at best, a mere recollection of some Biblical accounts. Are their efforts insufficient?
Jesus chose men to teach. He never told anybody to write anything down. He chose twelve men to replace the twelve fathers of the twelve tribes, to be the new twelve leaders of the new People of God, joined together no longer by blood but by Spirit in the New Covenant,
The men he chose to teach (apostles) he imbued with the Holy Spirit and Authority, so that they would not teach errors after He left.
Through the "Laying on of Hands" that authority has been passed down generations to the bishops. This is called "Apostolic Succession."
So, authentic teaching is preserved by the Holy Spirit and those authentic successors of the apostles.
Therefore, to answer your question, while it is good to read the Bible and get spiritual nourishment from the reading, one must never take it upon themselves to think that they can decide what is correct and incorrect doctrines based on their own personal interpretations of scriptures. That authority resides with the bishops.
Could a Christian get by without ever reading biblical text? Is the Bible really necessary?
Yes, we can get by without it. We have what Jesus established, His Church. Besides, the vast majority all Christians in history could not read anyway, from villagers in Judea to peasants in Medieval Europe.