As they are insect hunters, yes their absence would fuck up our already damaged ecosystem. I would guess it would lead to a different insect getting out of control and causing tons of problems - like a non native leaf miner who then proceeds to multiply like crazy and obliterate all leaves off trees kind of deal.

Anti-mosquitoes first please. I have yet to hear a single good point in defense of mosquitoes (unless they just went down the memory hole.)