Now you need a garbage collector for your indices and have reinvented object oriented programming via references.
That’s not a bad thing
I'd love to know more about how different games deal with deletion. Like I assume some (most?) allow generational indexes to dangle, and so any lookup might fail or return null or something. But maybe others try to aggressively clean up dangling references, and their lookup API tries to be infallible? I have no idea! :)