Well, there are those who claim that there’s no other way to attain Spiritual Liberation than to approach a Guru, others say that you don’t necessarily need a Guru, and others again who claim that you don’t need one, but that it makes your spiritual path easier because the Guru can see what you need, and support you by giving you the right instructions or tools.
The main argument for needing a spiritual Guru is that you need somebody who sees rightly and somebody who can convey the message. That is, if you’re blind, you need somebody who guides you, and you also need to hear of the message before there can be any spiritual quest at all.
Nevertheless, the message of Advaita has been conveyed for centuries, and, for instance, you may stumble upon it through reading something of an already deceased Advaita Guru. In fact, a deceased Guru can become your Guru. As it is, according to Advaita teachings a deceased Guru doesn’t really exist, nor does a living Guru, or alternatively they both exist concurrently (a spiritually enlightened one never dies), it’s just how you look at it.
Hence, I really don’t want to juggle with words here, but as has been said in Advaita: “Everything happens in (your) consciousness.” As such, the teaching of a Guru who isn’t “among us” is available and may be sufficient for you.
However, the advantage of a living Guru is that you can pose your specific questions to him or her, and they can help you to avoid “traps” and bring you back with your two feet on the ground. A dead Guru will probably not correct you if your conceptual thinking takes you in wrong directions, as it were.
Additionally, the Guru for you may not at all be in the form of a human being, or he or she may only be necessary for a short period of time. It may turn out that your Guru is Nature itself, a certain profound experience, a seemingly insignificant occurrence, or whatnot. That may be all that’s needed to launch you on your spiritual path and give you the necessary guidance.