well look at it like this
if you cold approah 100 women, you'll get 50 numbers, 25 of which will be real and will answer your texts, 10 of which aren't just wasting your time and will go out with you at least once, 5 of those 10 will eventually have sex with you.
would you be concerned with the other 95 girls? if you don't put women on a pedestal you'll realize that the 5 you got are the same as the 95 you didn't, so you didn't miss out on anything you didn't get.
but in theory, you can re-attract a girl. in practice you would need her to either still be willing to go out with you or still be willing to talk to you, if she's not your chances are 0%, but if she won't go out with you but will still talk your chances are low, single digits, but still there.
the other and main thing you need, is for whatever caused her interest to drop to be fixable/temporary, but you'll never know what made her interest fall, if you fvcked up you can fix it if she lets you, but what if you didn't fvck up?
what if it's not your fault at all? you can't really fix her ex coming back or her deciding she's a lesbian or a hotter guy starting to talk to her that day, etc. and you'll never know if you fvcked up or if her ex came back.
main point: it's not worth the effort and not likely to work out
but in the ideal scenario where she still talks to you and you know where you went wrong, simply game her good, be alpha (unless your problem was being too alpha), don't make any new mistakes and fix the old ones