The past 43 years of "canon" is still around for fans and indeed newcomers to look back on and enjoy. When some people go and see the film, they will just walk out and go on to the next blockbuster film release. Others will really enjoy the film and come to the realization that there's more where that film came from and go on to explore the rest of the Star Trek TV series, films and other material. It will hopefully keep the flame alive.
I can be an incredible nitpicker of canon when it comes to sci-fi - for instance, inconsistencies in the portrayal of aliens and "the conspiracy" in The X-Files mythology stories used to get me really annoyed (first killer bees carrying smallpox, then an alien virus, then grey aliens as black oil and cyborg super-soliders? Come on!), and the various deviations from canon in Enterprise initially annoyed me too (where the hell where the Xindi in previous shows? Where?), but after a while I came to the realisation that this will ultimately happen with all popular sci-fi: there are different versions of it.
This has happened numerous times to the DC universes, and Marvel has god knows how many timelines floating around in it, and yet in both, people are still working with them and making new content. The same can be done with Star Trek as well - it's just as durable as a universe and an idea as the rest of them. The "old canon" can exist, alongside the new one started by this film.
In fact, I cite the precedent of Doctor Who, another equally long running franchise. The revival of that show in 2003 came with the concept of a Time War that wiped the slate clean of most of the old trappings of the show, such as the Time Lords and redesigning popular races such as the Cybermen and Daleks within the context of the new show. Some of the older and more dedicated fans cried foul, declaring the producers were destroying their beloved show, and then? Several years later it's going well, more popular than ever with the new TV show's continuity existing in tandem with a wider universe of books, audio plays and other productions set firmly within the canon of the old series.
The same can happen with Trek. There's room for both old and new within the franchise, and no doubt in several years time people will be arguing about canon within the new universe after Trek XII, and canon within the other Trek Prime universe as well with new material being produced from that.