Nobody should lie, but especially not in your workplace. Some things don't last, and I think a lie is one of them. If we take this situation that happened, we can confirm that no liar is as capable of maintaining a big secret for a long period of time. Dan, the star of this novel, decided that it was a good idea to tell HR that his mother was very sick and needed his care for a month. He did, of course, to ensure a paid leave… but he was not going to her house. Instead, he had planned a luxurious trip to Bali weeks in advance, and needed the time - and the money - to go and enjoy.
Because his leave was not going to last long, a coworker decided to cover his workload until he came back. They did this out of respect and love, considering that it is an enormous amount of work, but really wanted to help him in this time of need. Little did they know that one morning, when they had to access Dan's computer to check some information, they were going to encounter the itinerary and a detailed schedule of what he and his family were going to be doing in Bali.
But seems that care is still there, because now the OP is hesitant about going to HR and exposing Dan. On one side, they cannot handle any more work, and they have started living with constant stress due to tight deadlines and a double amount of work. But on the other side, there's no sick parent, and he's out there enjoying a holiday on the other side of the world. If you ask me, I'd definitely expose him because there's no way that I'll keep doing someone else's work… not when they lied about a complicated family issue. He deserves to be fired… Mmm, I thinks is affecting me more than it should. Okay, I'll be quiet now; go ahead and read the story.