I didn't realize Rylan could die fighting the Overlord, but I'm not aware of any way to revive anyone in the game. There may be a way to change flags in game files, but the game files are archived, so you'd need to unarchive them and find the correct flag (if there even is one, which I don't know). But it also sounds like you aren't very far into the game anyway, and restarting is honestly probably faster than unarchiving the entire game.
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Yeah, that's what I just did. I'm kinda pissed at myself for not paying attention, wanted to load a save and accidentally saved over it without noticing. Thanks for answering though!
About Rylan dying, was because my dumb ass put him in the front with Bradley. I don't know why I did it, I just thought since the game allowed me to mess up with the positions, why not, lol. I'm gonna leave it as default next time.
Oh, no, no. When the fight was over a couple of crewmates (Bradley and I don't remember which others) said something about him not making it, and that's it. I found it weird that no one else brought the subject after. As I said his room dissapeared, his icon in the salaries interface dissapeared too. When I wanted to talk with his brother after the Warlord fight it said that I had to talk with Rylan first, and what confused me more was that I still could choose him for companionship in fights. Then I searched everywhere without any luck. Maybe the developer(s) just haven't expanded more on that side. I suppose it'd be the same for other characters too, I'm too lazy to check. In the end I just restarted because yeah, it's faster and easier as you mentioned.
It's probably an oversight. I've completed the game twice already and now I'm testing other options and paths. In a new run I left Rylan in prison until after I defeated Arihama. When I released him, he talked as if he participated in the fight. Then when I went to visit his brother with him, it didn't give me the option to go to Riordan's house after leaving.
Now I'm curious to see what happens if other characters die in the Arihama fight, will test that later.
I... don't think there's even supposed to be a way to complete the game yet. If the end is programmed already, it's probably supposed to be inaccessible, but can be found through some bug.
Also, I got the impression you weren't far in at all, since the scenes you're talking about are early game scenes.