You can get oil analysis done to prove the oil is good. I have never heard of an engine failure where the owner was on a legitimate oil change cycle... whether it be 3k, 5k or even 7.5k. Use a quality synthetic oil, stick to a good schedule and don't stress about it IMO. If you do happen to have a major failure (unlikely) then grab a sample and have the oil tested. That will either prove to your warranty company that the oil wasn't at fault OR if it was, most oil companies have their own warranty and should cover you there.