I think if Freddie ends up with no one it would make everyone even more upset the Creddiers and the Seddiers will be pissed that he ended up with no one. I honestly don’t think Dan would leave the Seddiers hanging after Sam and Freddie saying "I Love You" to each other and not let them end up with each other.
He has spent so many years showing us their character development and the Seddie hints i.e. Sam’s face at the end of iSpeed Date, iKiss, the Seddie Arc, etc. he wouldn’t have put so much effort into these episodes if he didn't want Seddie to end up together. I mean for iKiss he could have easily made Freddie kiss Carly in the studio when they were alone talking about their first kiss instead of having him kiss Sam but he didn’t, he also could have not had Sam have the depressed and hurt look she had at the end of iSpeed Date, in iSaved Your Life when Freddie told her “She just couldn’t stand the idea of Carly and him as a couple” instead of her saying “very true it makes me want to puke up blood” he could have had her say “no im happy for you both” but he didn't. Why? Because I believe he has had the intention of Seddie happening from the very beginning he wouldn’t have dedicated an entire arc to their relationship to show how it would be if they dated if he didn’t have the intention of them ending up together.
And their break - up was by no means platonic you all saw their break - up he wouldn’t have made them say i love you to each other if he didnt have the intention of them ending up together and it was made perfectly clear that they didn’t want to break up but they thought they should because they felt like they had so many obstacles against them at the moment and thought that they both need to mature and then they will get back together.
As for Creddie I honestly don’t see them getting back together after iLove You happened. Freddie would seem like a complete jerk and it would be completely OOC for him to get with Carly after he said "I Love You" to Sam (because Dan said Freddie is a good guy) and Carly wouldn’t get together with Freddie she wouldn’t do that to her best friend. I think what Dan meant when he said "everyone will be happy at the end of iCarly" was that he would make the Creddiers have closure by maybe making an episode where Carly & Freddie discuss their feelings for each other and that they decide to just be friends because they both no longer have romanitc feelings for each other.
Also, Carly never returned the feelings Freddie had for her think back to iPilot Carly said to him “i told you we can be buds but you got to get over this crush you have on me.” and whenever he said he loved Carly there was always a laugh track playing showing that his crush on her wasnt meant to be taken seriously but as a joke. However, when Freddie said "I love you" to sam there was NO laugh track showing us that it was a serious moment between two people who love each other so much. So, that’s why I think that Dan won’t make Freddie not end up with anyone of the girls and why I think Seddie was Dan’s ship from the very beginning ;)