My answer is no, crashes are not inevitable. They do happen to most of us at one point or another, but you can go for decades between crashes. I hate it when people say they are inevitable, or repeat trite sayings like "There are two types of riders..." or "Winners never quit." and then actually believe them. They are just generalizations, not truths.
I think that a lot of the time, an attitude that you can't prevent all accidents can lead to less effort in preventing them. A lot of people just think that if it's "Your Time", you are going to bite it. To me, that's just another trite saying, just another stupid generalization that people use to let themselves and others off the hook when they lose focus and bin it.
I've been riding sport bikes fast for more than 30 years, and done more than 100 days at the track. Yes, I've crashed a few times. Every time, I did something that was less than ideal to contribute to the event. I always try to keep improving my handling of situations to bring it closer to perfect. I know I can't be perfect in real life, but I have crashed one hell of a lot less than others who haven't worked as hard on trying.
So I like to tell myself that all crashes are preventable even though intellectually I know that something could potentially come completely out of the blue to take me out. But the vast majority of things that cause crashes are not so unpredictable.