I would think it depends on how well they know the person and If they really like you I'm sure they feel rejection and add it to the sky high pile they have already . I was freinds with my ex BPD gf for 4 years before we got together and she made it clear that she liked me in that way from day 1 if I had if dumped her in idolisation phase I think suicide would of taken place not a threat ! I think if they just grab someone after being dumped without knowing them then it prob doesn't affect them much or another point of veiw is it depends if they got dumped my someone they really did love after a long relaitonship then got dumped by someone that early on would be like a double whamy !
My ex has just done this she reached out to me with in 6 weeks in idolisation phase having massive arguments and him belittleing her and being horrible to her it's like he knows he can do that as she adored him let him move in instantly as he was homeless and just taking the piss ! And she just took it as she can't be alone my replacement prob thought it was great until 6 weeks in and now she's giving all the hatred , anger etc back to him he pretty much dumps her every weekend and leaves to then return the same nite as he reminds himself he's got nowhere to go and prob regrets getting with her

I can see them 2 canabalising each other ! Then her kicking him out to then never return Ther arguments are so bad the police were called by Ther neighbour on Xmas eve and causing disturbance of the peace oh well his prob now not mine