There would be impact but if anything human are good with adapting and with technology. Is it impossible to image that these million species roles can be replaced with technology ?
This is an honest question: do you really see no issue in replacing bees with robo-bees? Do you really believe humanity can just technology our way out of every issue we face? What happens when the whole system collapses?
Personally, I have a moral issue with it. Bees are living creatures. No amount of tech will ever replace the beauty of a living, breathing creature. This moral issue can be translated to any other creature that we are affecting. They depend on us to be good to them and treat them with the same respect we show any other creature, and we depend on them to sustain us and the planet as a whole.
If we are not able to organize our behaviour in a way that don't destroy the existing working system, why do you believe that we will able to accomplish, the arguable most difficult task, of creating a working system anew?