That's not how gravity works. The "kicks" from star death aren't shooting them to the outside of the galazy where they just park.
The "kicks" are just tranforming the galactic orbital path from the typical "visible star path" to a different set of paths. The objects still would pass through the visible layer at some point, so the lensing events would still occur.
You know, assuming the described calculated results are true.
When the remains form surely they contribute to microlensing. But after they out of the visible Galaxy boundary, they stop. And given the end up 2-3 times from the boundary, they spent the vast majority of the time there without contributing to lensing.
Now consider that according to the paper 30% is going to leave the Galaxy. Those after the initial travel will never contribute to anything.
The "kicks" are just tranforming the galactic orbital path from the typical "visible star path" to a different set of paths. The objects still would pass through the visible layer at some point, so the lensing events would still occur.
You know, assuming the described calculated results are true.