The most serious death threat for ELL has been:
TPTB will be watching this very closely and if we basically create a copy of ELU, they will shut ELL down before it sees the light of public beta.
EL&U had decided not to migrate questions here yet - to let us constitute ourselves, define who we are without them butting in with questions "they don't want", and instead encouraging askers to come here through comments.
But what about migration in the opposite direction? Questions too advanced for ELL and simply matching ELU better happen and will happen.
Technically, so far, before a migration path is established, this is done by picking "Flag", "it needs ♦ moderator attention", "other" and typing "belongs to ELU". Once several such migrations happen, a path will be created.
Still, the question is: Should we?
My personal opinion:
While ELU has nothing to lose by not migrating "our" questions our way, and I appreciate their courtesy of "letting us define ourselves", we have everything to lose by not shaping ourselves to be different than ELU, so count my vote as "yes".