I've heard/read that if one switch is bad, neither one will work.
On my 97 crew cab, the front passenger door would only lock with the key, not the door handle slider. Was that way when I got the truck.
Recently that door decided it would not lock with the key either! When the power locks work(infrequently on this truck) all four doors would lock and unlock with either door switch. The switches act dead, but after swapping out the passenger side one with one I got out of a nice burb at the yard, I can get it to click , but the locks still don't work. After the trip to the yard, to explore how the doors work, and further work on my truck, I discovered that the actuator on that door has frozen in the "unlock" position. The lock rod from the slider to the latch has a short vertical arm on it, that goes into the actuator linkage. By popping that rod out of the linkage, and lubing the moving parts with white lithium grease, I am now able to lock the door or unlock it, with the key or slider(I replaced the inside handle assembly, it had something broken inside the slider).
Here's some pictures to help explain how it works: