As the story is completed, is there any more development with the side characters then? Meaning that certain actions in the main branch will open up options with them again? Or should I ignore the tabs now because there will not be shown any more options until the end.
Depending on whether you interacted or not and how you did it the MC's partners will have a different ending, and the MC will have a different ending depending on the relationships he/she has had in the whole story.
A lot of time has passed but as I remember depending on the relationship that the MC has, one ending or another will be activated, if you want an ending with X character don't formalize relationships with other characters.
My favorite ending is with the mother and sister, badass ending like few I have seen.
He has since gone on to expand two new, extraordinary games in a similar vein and I strongly encourage trying them out as they are awesome! Though in a selfish way this game has a special place in my heart and I always hoped he'd return to it... but if a developer is not enthusiastic, it would be an anemic game anyway so best to follow to the new and awesome things!
I would have liked a sequel to this game too, mainly because the MC seems to me to be one of the most badass characters I've ever seen, but with so many endings it's understandable to leave it at the end.
Besides, now he's working on the sequel to Occultus, which isn't bad either.