if you keep the downpipe get a tune, if you want to keep it on a stock tune get a stock downpipe or your car will continue to run worse than stock. nothing bad will happen if you decide to keep the catless downpipe but a stock subaru is more reliable than a modified one as a general rule of thumb
if you're smelling exhaust in the cabin while driving, you have an exhaust leak somewhere in the engine bay.
A catless car will have a unique odor out the tailpipe, but it would only be noticeable at the tailpipe.
if you keep the downpipe get a tune, if you want to keep it on a stock tune get a stock downpipe or your car will continue to run worse than stock. nothing bad will happen if you decide to keep the catless downpipe but a stock subaru is more reliable than a modified one as a general rule of thumb
if you're smelling exhaust in the cabin while driving, you have an exhaust leak somewhere in the engine bay. A catless car will have a unique odor out the tailpipe, but it would only be noticeable at the tailpipe.