it would still project a new timeline instead of fixing it, oh how time consequences are fun to mess around

if he finds out what she could have changed he would have to make the change never happen, and still it would produce a new timeline, that wold be similar to the previous where the change never happened, but there would still be a change, each change already done make a domino rule,
Lotto numbers<
Lotto numbers<Card Numbers<
Lotto numbers<Card Numbers<phone change<
Lotto numbers<Card Numbers<phone change<Gender Change<
Lotto numbers<Card Numbers<phone change<Gender Change<Event Change<
Lotto numbers<Card Numbers<phone change<Gender Change<Event Change<Next Change
from farthest change to nearest, all changes produce new timeline and new events and their consequences, additionally, in every time the result could become different, when he was asked for a phone change D-Mail the lotto did not happen, but we don't know which events do repeat or don't because not all are mentioned, the paradox will keep deepening and
ultimately he will lose his mind completely.
there is no stopping that, the only way to actually stop all this madness is ... killing Kurisu since she increases their lab's overall productivity with HER genius and one more thing.
The Part timer seems to also remember events happening, she doesn't bother herself with that since her priority seems to be getting rid of Kurisu. And i think this is the target of this show.