DoomRL games are mostly winnable, but there is no guarantee that every game you attempt is winnable. This is a part and parcel of the whole rogue-like genre, and it comes from the fact that the "level design" is mostly controlled by a stochastic process -- there is no "overarching intelligence" that is balancing the game such that a win is virtually guaranteed. Now, with that out of the way, let me say something about AoPc.
HR is key for AoPc. Moving fast in-game and using side-stepping (walking diagonally) helps much more than trying to hide. In normal games, hiding is good because you have a means of retaliation (i.e. shooting at them), but in AoPc you have nothing you can retaliate with; I remember one time where I was stuck in the Halls of Carnage sandwiched between two Hell Knights(?) and having to just wait for them to kill me because I couldn't do anything else in AoPc.
In AoPc, you must always advance, but never walk directly into the line of fire. Diagonal walking is your friend, and once you've get the hang of that, just enjoy the many runs through hell. It's not even a game of GOTTA GO FAST TO THE EXIT. It is FIND THE EXIT WHILE EATING LESS DAMAGE. Sure, it might take 20 to 50 games before you have one success, but that's just how a rogue-like is defined by.
