Questions:

If I book a multi city flight as shown below over e.g. SEAT24 (I found this on momondo),
and I then decide to skip the middle flight from GRU to SCL, but buy me a new one separately a few days later with different airline,
will the last flight from Lima to Dublin be canceled? Or can I still use it?

DUB-GRU 1 stop in Madrid with Iberia
GRU-SCL nonstop with LATAM
LIM-DUB 1 stop in Madrid with Iberia

Thank you