island vent

Plumber installed an island loop with this setup. He says it was done this way because connecting the vent back to the drain would cause more damage to the slab (this is a reno and we had to cut about a foot deep into the slab to make this happen). What problems am I looking at down the road?

Hello, long time reader, first time poster! I really like this site and appreciate Terry and all the other guiding lights here. Thank you. I wasn't sure if I should join an existing thread or start one, I couldn't find a recent one that made sense so new thread. Apologies if this is not cool. I...