Just purely on religious purview alone, the Hebrew language is so valuable and honored amongst millions of individuals, most of which who do not even speak it. It is almost holy in its origin, forever connected with the foundation of Christianity, Jesus, Israel redemption and the Bible. Even dead languages are magnanimously valuable today as we continue to learn and educate ourselves about history (an underrated source/faction of knowledge). This is all aside from the fact that their is an entire nation that still speaks it as the dominant, most widespread language amongst its people, and it is technically still the official language of Palestine. Regardless, whether or not it is kept in what may be deemed as a cultish manner, a language can truly only be dead when it no longer becomes of use, and that will never happen with Hebrew.
Although a lot of languages have 'died' over the course of human history, many have stood the test of time. It is not certain that Hebrew will be frequently used in the coming decades. However, today we have the ability to store enormous amounts of electronic data. That is not something that generations of humans had. So, although Hebrew may not be widely used it will be available electronically to be called back up and hence it will never 'die'.
I think because of the amount of people who still speak Hebrew it will survive the 21st century, however I would expect it to continue to decline. It has been declining over the years and there is nothing to suggest it will start going the other direction with more people speaking it.
Despite the fact that Hebrew was essentially considered to be a dead language in the first half of the twentieth century, this has all been turned around because of the ideological bent of the state of Israel which promoted its use unsparingly. Now, there are individuals in Israel who speak nothing other than Hebrew. This alone will ensure that it will survive for a long time to come.