Question about SG ending

I have just finished SG and SG0 and let me preface by saying it was awesome. However my brain still has a hard time comprehending the ending of SG. I understand that Okabe sends the D mail to daru with the belief that kurusu is actually dead even thought she is alive. Wouldn’t this send him back to the Alpha world line and allow sern to identify their messages and infiltrate the lab again thus leading to myuri death once more. Or is the fact that kurusu actually lived enough to make his transportation take him directly to SG worldine? And when he reaches SG does his memories get overwritten by the okabe we’ve seen for the majorly of the show. And finally do the rest of the lab members know who kurusu is in the SG worldine? Thanks in advance and sorry if I’m missing something obvious time travel not my strong suit😅