The short answer is: We don't know. Earthquakes cannot be predicted with precision in terms of exact timing.
However, we can make probabilistic assessments. Seismologists estimate there is approximately a 30-50% probability of a magnitude 7.5-8.0 earthquake in the Mexican subduction zone in the next 50 years. This means it is likely, but not certain.
The Guerrero seismic gap is particularly concerning. The last major earthquake there was in 1911, 115 years ago. Historical patterns suggest intervals of 100-140 years. Mathematically, we are already in the expected window for the next major event.
What we CAN say with certainty is that another major earthquake WILL come eventually. Based on geological patterns, it is almost certain to occur within the next century. It could be tomorrow or 30 years from now.
This is exactly why preparing now is so important. Don't wait to know when it will come; prepare as if it will come at any time.