I have absolutely zero reliability concerns with Glocks over time. Springs break from repeated cycles, not staying compressed. The torture tests are practically legendary. The Temifer finish is super durable and actually penetrates the surface of the metal. I live in South Florida and used to pocket carry my Glock 26 all the time. I do have some wear on the slide to the point the finish has worn off. Despite that, I have had zero issues with rust.
As someone else mentioned, the G19's mags can be shared with the G26. I would much rather stock one type of ammo rather than getting another caliber. It is easier to make bulk ammo purchases and 9mm is still fairly reasonable.
Good choice keeping your G19!
The ATF should be a convenience store instead of a government agency!