If one realized he concluded the first brocha of birkas hamazon with “al haaretz v’al hamazon” and did not correct himself b’toch kdei dibur, seemingly the whole brocha should be repeated, correct? And what if the person didn’t know and instead returned to the middle of that brocha (instead of the pesicha) and continued from there, concluding with the proper habrocha this time and the rest of benching; is he yotzeh bidieved?
On the surface it would seem that the person would have to bentch again, because what he said was a hefsek in the first bracha. However, I was tallking with big talmid chacham abpout this question, (Horav Y. Cahen, a Rov dayan and Rosh Kollel in Kiryat Sefer) and he told me an interesting story that happened to him years ago. He had a guest that made a similar mistake with Ritzei and in middle of bentching he didn’t know what to do. At that time this person lived on Rechov Rashbam in Bnei Brak, he knocked on a few people’s doors, but no one could answer him, so he decided to knock on the door of the Steipler. The Steilper told him, that since there is still a safek that he might have been yotze, he should wash again and eat a kezayis of bread. Then, the Steipler concluded, “I do this often, whenever I have such a question”.