Motor neurons dying != brain control of motor neurons dies.
Anyway, you don't need a brain-computer interface for an ALS patient to work. I have a friend in Finland with ALS who works as a consultant on safety for a nuclear reactor startup (he was a nuclear safety engineer before becoming paralyzed). All it takes is an eye tracker.
The biggest problem is the typically short and unpredictable lives of ALS patients. He has lived abnormally long (I think something like 13 years now), but a large part of that is due to him thinking like a nuclear safety engineer (backup on backup on backup, training his nurses to have zero tolerance for error, etc), and still has a close call like once per year or so, and I regularly worry when I don't see him online in a while that something happened that killed him. A tube comes off a life support system. A nurse forgetting to reconnect something. A mucus plug in his airways. Etc. ALS patients' lives are fragile. He does CAD design for parts on his computer (it's too hard to do it with the mouse using the eye tracker, so he designs the shapes programmatically) and orders them 3d printed to correct any deficiencies he finds in his support systems.
ALS patients also have to constantly fight the medical system. Even in a place like Finland that will actually do long-term care for ALS patients (which is very expensive), it shows that it would be much more convenient for them if those danged ALS patients would choose to die (and there's often pressure put on them to do so). One of my friend's goals is to outlive a doctor who told him he would only live a year or two put a lot of effort into getting him to choose death. It was a battle to get long-term ventilator care. It was an even bigger battle to get to use a cough machine and to be able to control the settings on it; without regular, meaningful cough support, your lungs fill with mucus, and you'll probably eventually die of a mucus plug, pneumonia, or whatnot.
By contrast, ALS patients today can actually live a decent life using eye trackers. It's not like before when you had to tediously spell out things one character at a time to a helper holding an E-tran frame. Given that 1 in 500 people will get ALS at some point in their life, we really should be allocating a lot more money toward researching cures, even if purely from a cost-saving perspective.
(One final note: if anyone here starts getting peripheral weakness and worries its ALS: your instinct will be to exercise more. Do just the opposite. If your peripheral neurons are dying, the last thing they need is more work. ALS overwhelmingly strikes active people - one researcher I was reading noted that in her entire career, she's never met a couch potato who got ALS. Take it easy, see a doctor immediately, and if it is ALS, start preparing early, but know that you do not have to be forced to choose to die, so long as you can get care. You can live a decent, productive life if you choose to).
