I personally thought last time that Rito was lucky in this matter but if he pushes his luck, and chooses Haruna over all the other girls, and stays with only one girl I don't think that Lala will be able to stop the retaliation of Gid towards Rito and Earth because it is well known that he cares for his daughters a great deal, and he will be very pissed at him.
Possibly. However, I'm not entirely sure if he still cares much about the relationship status of Rito and Lala, since that was such a long time ago he was desperate to get the pair married, and he never even brought it up when they met again in Darkness chapters 59-61. However, he could at least get angry if he finds out he has broken her heart.
If Rito does break their hearts, I personally hope Gid would retaliate. Rather than destroy Earth and kill 7 billion people, he should destroy Rito, Haruna and ISIS in space.
This will end up very badly because Gid is very overprotective about his daughters, and he hates seem them in pain because Momo will be crushed that is to be sure, and Lala might even feel it worse than her.
I am starting to get in a mood to bash Rito right now in the current chapter Nemesis did the right thing in making this come out in the open but like a typical wuss that he is the guy can't accept the Harem if that was the case why in the hell you kept Lala in your Home.
Rito is a selfish bastard and a wimp it is stated in the story that he kept Lala as a insurance policy if things don't work out between him and Haruna I wonder if he truly loves Lala because Haruna is a nice girl but in terms of personality Lala simply outclasses her in all departments.
Haruna is the only person that can resolve this problem if she is a good person like I think she could literally force Rito to accept the Harem by saying that if you don't accept Lala as the second girl in the equation I will not be in a relationship with you anymore.
Rito in my opinion is not designed for Harems he doesn't have the personality and traits to handle this I actually thought that Ichika from Infinite Stratos is worse than him but now I am not too sure.