With the new auditing rules that took effect 01/01/2018 affecting partnerships under 100 partners, I doubt the Irs would try to assess any penalties as long as all profits and income was reported on schedule C. I would count on the amended 1040 would be sufficient. In fact prior to 2018 a small partnership (under 10 partners) did not even have to file a 1065 see    Rev. Proc. 84-35. Almost forgot the "foreign partner" would have to see what he put down, as that could open a can of worms. That is the trouble with answering questions here, as all of the facts are never known, and knowing the exact and complete picture can change your answer