Boeing is staring down the barrel of BOTH MAX and NG being grounded. And that might very well be the end not only for the 737, but for the Boeing Company.
The NG has nearly 7,000 aircraft in service and has been in the air for 22 years with
zero crashes due to runaway trim.
The chances that the NG will be grounded:
zero. It has proven itself to be a very safe aircraft.
With MCAS disabled (post fix), the MAX's safety profile
from a trim runaway is the same as the NG.
The "end of Boeing" scenario being posed here is pure fantasy.