I think they r simply fullfilling AR fans demand.
Of getting AR married.
If Armaan would have know the truth lyk tat only by Ridz than he would blame himself for Ridz condition,the condition in which she married sid forcefull becoz of him not being there.
He would probably let sid n Ridz to be together married he won't even interfer in there lyf as Armaan only wanted Ridz happiness tat's it.
But now if Ridz marrys Armaan both sid n Ridz would be guilty n when Armaan would know the truth by someone else[may be from shanky when he would enter late in the scene after there marriage]
From tat time Armaan would be really angry on sid n Ridz for this.He may not talk with Ridz n sid.[would probably become rude]
After few days a new entry in Sanjivani a girl or may be Tam bak in Sid's lyf.
If a new girl than sid n her 1st be frnd than would start feeling for each other.
If Tam then sid will remember his 1st luv.
On the other side Armaan who still luv's Ridz but, can't forget wat she has done to him n Ridz still confuse??but after seeing sid happy with Tam/ngirl than she would again fall for Armaan..she'll try to tell sorry to him I think even sid will help her in this.
Than finally Armaan Ridhima will be together
hope u all lyked it.
P.s:guys it's just my prediction.
If hurt someone than sorry,nothing personal.