Darren's team build the portal to Carynrein and sends him through, he becomes a scientist for the King and Queen of Lyversdale and tries his hardest to get back. He is unfortunately bound to the royals and can't go back to look for his son, so that's part of the "secret task" Dr. Franks assigns for Robert.

Joseph killing Lockie is a cause for Timmy's fall, meaning his adopted son is sent to Darren's old lab, though he isn't around to prevent his best friend's child from becoming a Wendigo

Darren falling in love with Marienne leads to Joseph's birth, allowing him to go to Carynrein (against his will) in order to help save the kingdom from the Corrupted!Royals.

Mark's rough and abusive Marriage leads to Peter's birth and molds his personality into the timid and jumpy kid he grows up to be after witnessing what his mother does to his father

Darren's recreation of the portal leads to Robert meeting William Shawshett and Peter, both of which end up helping to save the Kingdom with Darren's son, and also leads to Robert getting married, which is a plus

Darren's efforts to save Joseph from getting turned into a Wendigo is what lets him keep enough of his humanity and sanity to be able to escape once, get blackmailed into becoming a hitman and kill Lockie when he's trying to propose to his boyfriend. It also is what allows Joseph to become the "Best Sniper on Earth" which attracts the Rebels' attention.