Well I guess Peter lost his salvation when he denied Jesus? Then somehow someone got the translating wrong in John 10:28 & 29? Maybe it should read "I give them temporary life, and they can perish. No one is secure in my Fathers hand. My Father can not keep a person form falling out of His protective hand. The Father who has given them to me, He is great, but he can not prevent anyone form falling out of His protective hand. The Father and I are one, but we have no power to give you anything, not even eternal security."
IMO if eternal does not mean forever, what does it mean? If we are saved and then can be lost, then there is NO WAY to be saved again, according to Hebrews 6:4-6. So if being out of fellowship means the loss of our salvation, please tell me who you know who is 100% of the time in total complete fellowship with Jesus Christ? If what you state is true we do not stand a chance of being saved! If the Blood of my Lord Jesus Christ is not powerful enough to save, and if the Holy Spirit living in me and sealing me is not a guarantee of my Salvation, and if the Bibles words in John 10:28-29 can not be trusted as they are stated in plane English, then we are doomed to hell!
Take time to use a good EXHAUSTIVE CONCORDANCE, like Strongs and look up the words in the back under the Greek Words section. Read each word in the verses and you will find just what "eternal" really means.
When you make the statement that being out of fellowship with Jesus we are not saved, you may need to prayerfully reread the Scripture, and ask the Holy Spirit to give you a clear understanding of John 10:28-29. IMO you might find something new and different.