It takes time (decades) for many of the effects of traumatic brain injury to reveal themselves. Look at the NFL.
Taking lots of blows to the head is probably not a good idea for your health, long-term. I doubt getting blood choked is good for you either.
BJJ has been around for over a century. Submissions date back to pankration. Outside of someone intentionally holding a choke for too long, I've yet to EVER hear of an issue as a result of a blood choke. Obviously, getting punched in the face isn't good for you. But, the inherent risk is grossly exaggerated as it pertains to MMA. Outside of the Travis Fulton, Jeremy Horn, Shannon Ritch style journeymen, very, very few fighters actually have the number of fights to really deal that potential for long term damage; especially with the current movement that is moving away from live sparring to a more safe style of training (read up on Hendricks' position on this if you're unfamiliar).