you're confusing some stuff.
the Knox warranty void counter WILL BE TRIPPED if you'll root your device, hence, your Knox app will not work on your device.
there is no possible way to reset the Knox counter as for now.
You won't get OTA updates, because your phone will change from Official status to Custom, though with xposed module: wanam xposed, you can trick your device to be official, and still get updates via the option there: fake system status.
you can always flash a new rom with odin, even stock roms of course... but you will have to root the device again.
triangle away will reset the flash counter, but it will not reset the Knox warranty void counter.
you can see that counter in download mode (pwr button+volume down+home button)
Knox warranty void: 0x0 (not tripped) 0x1 (tripped)