I mean Emet wants to bring back the ancients, the rejoinings and destruction of the shards are just the only way they have found that could achieve such a result.
Had a way to rejoin the people back into unsundered without the need for the destruction of shards he would take it.
I mean,who wouldn’t want that? Do you realize how much effort and time it takes for them to have a shard be towards a specific element and have the source be near a calamity level that fits said element? Like the amount of time and work to achieve this is ridiculous plus having to wait for the people to repopulate to prepare the next calamity, Emet and the ascians would literally jump at the opportunity to bring back the ancients without having to do all that work.
The shards could survive, the ancients would just recreate their cities in some place, after all the goal is to bring back the ancients, not bring back a specific architecture or structures, these can be remade, the unsundered people cannot.
Considering he also asks us if we ‘remember’ it is clear that he was expecting that after x amount of rejoinings we could reach a level of power only the unsundered were capable of. (Though again zenos with artificial sharingan also reached it)
And had that happened how would he go about it? What does out ability to handle the light prove? Ok we are near unsundered levels powerful? How does that help in bringing back the ancients?
He isn’t stupid, his logic can’t be ‘oh he is equal value/power to me hence a new path will magically appear because of it’
He must have an inkling of an idea of the possibility.