I wouldn't have concerns about the replacement transmission. The early issues you reported - failure to enter forward or reverse - were not uncommon to the 2017 and early 2018 9-speed. There are a couple dozen reports of that on this forum. They cleaned up problems with debris created in production and created a calibration update. I can't remember the last time I read of this. Most who experienced that got the calibration update or valve body / solenoid replacement and have been trouble free from that particular issue. What you experienced, the priors followed by complete failure, I can only recall one other case of so it is really, really rare. I'd have confidence in any current GM 9-speed. I bet the fixed up car will serve whoever drives it well into the future. Good luck with whatever you choose.