Well they kinda explained some their absence in the past few episodes. But here's what I really think:
Jake, Amanda & Trevor: After Tad's possible "death," they probably joined Joe and Mrs. Martin in Florida to start a new life. Since Joe mentioned on yesterday's episode that Mrs. Martin stayed with them while he came back to pine valley
Kendall, Spike, & Ian: Since Zach mentioned Kendall left him because she feared that her & the kids lives were in danger because of the mob, she probably sold Fusion and moved out of pine valley, probably joined Erica in LA for a fresh start. That is if Erica did go after all.
Krystal, Katy, & Jenny: With Tad and Marissa gone, Krystal just thought that she lost everything and Pine Valley was just a bad place for her especially with losing Babe and she didn't want to raise the kids there or be reminded of the bad memories so she left for a brand life and fresh start.
Ryan, Greenlee, & Emma: Ryan finally got a job offer out of Pine Valley (since I still don't know what the hell Ryan did as a job) and finally married Greenlee and just wanted a fresh start.