.....to accept NP engagement? I think not.
Milsi is still in PA mode and also suffers from partial blindness and deafness as well. Prachi opened her mouth and heart to him and the guy ends up getting a headache. Now the girl is petrified that she would be responsible if something happens to him because of her loud mouth. At this point of time if she refuses to get engaged to Neev, Milsi would suspect that what she had been telling was the truth and this in her mind is not good for his health right now. Her concern for his life over rides everything. So she may just play along.
Prachi never seemed to attach much value to the engagement itself as she does to marriage. Remember what she adviced Suki on the day of her non-starter engagement before Suki decided to take things into her own hands and elope with Saket. She told her to go through with it for the time being and she will come up with a plan to stop the wedding. Even in the case of MA engagement, although Baba was all worried about it, she assured him saying it is only an engagement and not the wedding. Although she was heart broken to see the engagement itself, she held her tongue and would'nt let any one let lose their either. So I dont think she would be acting out of character if she goes along with the engagement but I think she may not let Neev actually put the ring on her finger.
As to marriage with Neev, Prachi will never take that step for anybody, not even Milsi. Unless ofcourse the creatives have forgotten the basic nature of the characters they have created.