AFAIK Sev survived and later helped in forming Rebels and fight against the Empire. Boss and Scorch sided with the Empire but they were against it in their hearts. Niner and another CM from Omega squad joined with the rest of Delta and formed Squad 40, while the rest of the Omega squad fled to Mandalore and went on to fight the Empire.
Also it's worth noting I hate books. I read up on this after finishing RC a year or two ago on Wookieepedia. The only book I read in the past 5 years was SWTOR: Revan because, well, it's about Revan and it covers the events after KOTOR and KOTOR2 between SWTOR. The story continues in SWTOR through Flashpoints and later on through the whole expansion Shadow of Revan.
But when you think about it, the ending sucks big time. It happens right before the Order 66 and you just can't continue the story since they became Imperial Commandos. Since that point I have more respect for Omega Squad than Delta Squad.
But yeah, to this day Republic Commando is one of the best FPS games I've played. They sure made them different back in the day.