In short, Ted and the mom had their two kids before they got married. Barney/Robin got divorced, Barney had a baby with some random woman and realized the love of his life was his new daughter. Robin has not seen the group in yrs and she finally came on Ted/Moms wedding. The mom convinced her to come. Then we see Ted talking to the kids and the kids are all "You did not tell us this story because of mom. You told us this story because of how much in love with Ant Robin you are. Basically the mom died like I always suspected. The kids convince Ted to give Robin who lives with her dogs a call. Instead he goes to her with the blue french Horn and that's how it ended.