There are some discrepancies between what is explained in the cutscenes and what is written in the manual. The wound like rip is assumed to be the rift and Heron was sucked into it having being pulled from Arokh's back by the forces unleashed. I assumed the blackened pit to be the remains of the battlefield around the area where Navaros was killed. The rift crystal was never mentioned in the story but its revealed during the game it is what gave the runeblade its power.
It does read like Arokh and Heron were together when Heron died and this very question was put to the developers a long time ago. Their answer was that only one of them was on the inside of the rip (rift) and the other was outside and therefore his death had no effect on Arokh.
In all legends though, what is written can be different to what actually happened. I got around this by explaining in the Drakan novel that the text described in the manual is what the people of Drakan in Rynn's time thought what happened. Legends change over time as the story is re-told to generation after generation. The book Rynn finds under the temple could have been written several decades after the war for example.
In several previews of the game the storyline is slightly different; it mentions that Arokh manages to cast Navaros through a temporal rift. Going by the games, this appears to be what actually happened. Note that when it says the runeblade was broken in two, the two parts were actually the blade itself and the rift crystal. The wound like rip could be what remains after a rift is opened then closed which the rip would later heal in time.
The game manual and story were written by two different people BTW.
As for Delon, it is poor that it is never explained what happened to him. Originally, OOTF was to be a level or two longer and it was cut short and a crappy ending hastilly made up to meet deadlines. Surreal also had every intention of the sequel being for the PC as they had already started on it before OOTF was even finished. Seem as Sony took over, plans were changed and we never got to find out about Delon's fate.
In TAG, the only references to Delon is 'Just look at what happened to your Brother' (Zola Dane) and 'Her dear brother lost' (intro to game) so going by the final cutcene of OOTF it's assumed he is dead / trapped in the rift world forever. It's assumed Arokh couldn't catch him as the rift was starting to close up; if they didn't get out of there, Rynn and Arokh would also be trapped in the rift.
Edit: I found this http://www.adrian-smith31.clara.co.uk/Delons_Grave.jpg
image entitled 'Delon's Grave' originally from Surreal's web site - this proves he is dead but how Rynn retrieved his body we don't know.