notre dame half joining the acc killed their annual michigan and michigan state series, every now and then they do play. Same will happen with usc.
USC is different. There are 3 games Notre Dame absolutely does not want to give up. USC, Stanford, and Navy.
USC is Notre Dame's most historically significant rivalry. Plus there is the added benefit of the every other year trip to California. Stanford means so much because they play them in California when they have USC at home. So those 2 games give Notre Dame a recruiting edge of playing in Cali every season.
Navy is historically significant. There is a special arrangement between them and Notre Dame, dating back to WWII. I could see them giving that game up on an annual basis, but they would be loathe to do so.
Notre Dame's Big Ten rivalries were significant, but that was mainly Michigan State and Purdue. They never played Michigan much until the 1980s. But none of them offered any sort of recruiting aid, so they were easier to give up.
The Big Ten does now have a significant feather in its cap with regards to Notre Dame, with their addition of USC. They could really leverage that by also bringing in Stanford, assuming Stanford is interested in any way. I think it bears watching. Right now, if Notre Dame is to join a conference fully, I'd give the Big Ten the best chance, followed by the ACC, and then the SEC a distant 3rd. There is simply no common ground between the SEC and Notre Dame. Only money. The Big Ten can offer that plus all the tradition.