The South Koreans won't see it that way. There is a lot of distrust of the US. Time after time they've seen us fail to meet promises there and elsewhere in the world. This will be interpreted as the same.
So we're bound to keep ground troops there in perpetuity because...they don't trust us? And as for keeping promises, we've had their backs for 65 years -- not to mention all the blood we spilled there from 50-53. If they still believe we are unreliable despite that, then they cannot reasonably be satisfied anyway.
They have every interest in the world in not falling under the sway of the Chinese, so as long as we maintain the formal alliance and the air/naval base, I don't see them as having any other options. And the truth is that some of those Army bases aren't all that popular among a lot of South Koreans. The one wrinkle in that is the construction of Camp Humphreys, which is massive, and supposed to house a shitload of troops. ROK's are footing much of the bill for that, and probably wouldn't be thrilled with us leaving it.