There is a very (very!) small chance that there are isolated biomes that split from life's tree before what we call the last universal common ancestor (LUCA) and are still plugging along. But it's pretty much impossible that some sister-metabolism from the pre-DNA days could just 'struggle along' side-by-side what we consider 'biology'. When something out-competes another by factors of 1000x or 1000000x, extinction is the only outcome. It's not like elephants and ants finding different niches for billions of years; we're talking about systems of molecules where most of the building blocks are at most a dozen or two atoms and most of the feedstocks are less than 5 (CH4, NH2, O2, H2S, CO, CO2, etc). What's this poor, struggling cousin that we outcompete by a factor of a million going to eat that we can't eat better? Similarly, how does it adapt and evolve against its peers when 999999/1000000 interactions aren't against peers but against us and our self-contained, portable, self-replicating, weaponized Krebs cycle machines?