Been there (though not geographically) done that. My two rules: if high HR when resting, sit in the shade and drink until it comes down. I haven't peed in 3 hours, same, sit and drink until I do. Now, the tricky part is that this depends on the availability of water and shade. Yeah one loses time, but one survives to ride another day. Nothing quite like mountain passes at 105°, noticing that one's forearms are no longer damp and no sag option.