The Lord is more alive than dead

it further states that the flame can destroy a hero

This message is a warning, not a prohibition against further advancement. Yes, it says so, but with a clarification – if you get too close to the fiery Gates. Well, that is, right up to the hellish flame bursting out of them with the intention of saying hello to Kha-Beleth. Besides, you can easily run up to the altar/tavern, as comrade Gerter rightly noted.