The Impeller dispatcher stores a copy to a pointer it is given that survives the method call:

https://github.com/flutter/engine/blob/df619c6a5237c2f82fd48806be2cfaf621024759/impeller/display_list/dl_dispatcher.cc#L968

It hands the pointer to the constructor of its own Vertices object which just saves it in a field:

https://github.com/flutter/engine/blob/df619c6a5237c2f82fd48806be2cfaf621024759/impeller/display_list/dl_vertices_geometry.cc#L68

The data should be copied out of the storage it is given as nowhere is it stated that the memory that is pointed to will be valid once the method returns.