60-70% loss in GDP would mean the literal end of the country, it's a ludicrously large figure no one could ever rebuild from. This is a 7.7 earthquake; it probably is 6–7% GBP which is still significant.
If Myanmar had a stable and reliably growing economy, the world would be a different place.
Turning Myanmar into a country with a stable economy that could grow at 5% annually would be worthy of a Nobel Prize in economics.
Practically, recovery costs in the neighborhood of 60% of Myanmar's GDP represents many decades of development. Or enormous foreign aid from China. I'm not sure how valuable Myanmar is to China though.
That's assuming otherwise zero growth, or other nations standing still or stuff like that.
Also, 10 years of constant 5% growth is a lot to ask for in general. Maybe not impossible, but really hard. Now, think that you need to have 5% growth in the first year after the earthquake, in a devastated nation. Infrastructure destroyed, people killed. Lots.
It sounds pretty near to impossible.
These numbers have some meaning you know. It's easy to type "5% growth". Much, much harder to actually achieve it.
How is the dead part of the population being replaced in this scenario? Who is achieving this growth if the population is decimated?
I'm not sure about any of these questions, I am just pointing out how wrong it is to suggest that a -60% economic setback is historically fatal. The economy of Myanmar increased 8-fold in the last 30 years.