If there's no deal then the UK will have to implement the NIP while protecting NI from its worst effects. Anybody that thinks otherwise is talking nonsense. https://twitter.com/simoncoveney/status/1325899413638754307
I'm afraid that means ensuring goods flow from GB to NI without paying tariffs, ensuring no export declarations between NI and GB, and minimising regulatory checks on certain goods e.g. food. This is the minimum I would expect.
If the govt didn't intervene in these circumstances then they would be standing back while NI businesses go to the wall and NI consumers face higher food prices. Put simply it is not going to happen.