Can a once truly saved believer backslide too much and lose the gift of salvation? If so do they need to repent and ask for forgiveness through Christ again? Thoughts are welcome and scripture too!
Actually, there are only two groups of people. Those with the ongoing "Fruits". or habit and way of life actions, attitudes, responses that prove them to be true Christians, and those with the "Fruits". or habit and way of life actions, attitudes, responses that prove them to be still lost and headed for hell, in spite of their belief that Jesus is their Lord, God and savior, and even with all the same signs, wonders and miracles the true Christians of the 1st century possessed. Jesus says each group is distinct and can never possess the fruits of the other group. Mat. 7:15-23 And Jesus says those who truly are true Christians can never exhibit the fruits of those who are lost in the same passage.
Noone ever "Loses" the fruits of salvation once possessed, and no one can keep the fruits of being lost and headed for hell once they change groups. Unless Jesus lied, those backsliding who do not physically sick, weak or die as a result, (1Co. 11:29-32, Example: 1Co. 5: 1-5, Not to pray for those who are sinning unto death 1Jn, 5:16-17) never were true Christians. Heb. 12:6-8 ... and, according to Jesus in Maty. 7:13-23, almost everyone who believes themselves to be Christian, even with all the signs and wonders of the true Christians, are still one of the "Many" on the broad path that leads to destruction, and not one of the few on the agonizing path that leads to the narrow gate that leads to hell.
This is not about having become a true Christian, and then losing your salvation or "giving it up". Those in this category never ever were saved in the first place, regardless of what they believe or don't believe.
Mat 7:23 "And then I will declare to them, 'I never knew you; DEPART FROM ME, YOU WHO PRACTICE LAWLESSNESS.'
1Jn 2:19 They went out from us, but they were never really of us; for if they had been of us, they would have remained with us; but they went out, so that it would be shown that they all are not of us.
Ther problem is, there are 10,000 different belief groups in the world, one of which is Christianity. Christianity has 45,000 belief groups in it, all with differing and conflicting core beliefs. (Or they'd be in with one of the other groups.) and every person in the world, Christian, or Not, believes they both love truth and have the truth (Or enough of it) to hold fast to their current beliefs as truth, and to reject all opposing beliefs as lies. Thus, the standard of evaluation of themselves and others to see if they have truth and love truth for all these belief groups is, do your core beliefs align with those of myself and the group who agrees with me.
Unfortunately, that's 10,000 different non-Christian belief groups judging each other's beliefs based on this standard, and 45,000 different belief groups evaluating the salvation of themselves and others based on their own beliefs. For every group evaluating salvation by their beliefs, God says they have absolutely no understanding of the topic of salvation at all.
2Co 10:12 For we are not bold to class or compare ourselves with some of those who commend themselves; but when they measure themselves by themselves and compare themselves with themselves, they are without understanding.
"Backsliding" of a true Christian is not a thing. True Christians don't, unless they are sick, weak and/or heading for physical death. True Christians are judged now. They don't lose their salvation, even if they are actively performing sins even the Gentiles would cringe at, and are also non-repentant. See 1Co. 5:5. God reproves those He loves. There is no becoming a non-child after becoming a child. If you are a child and misbehave, sickness, weakness, or, if you really misbehave, or keep on misbehaving in minor ways, and fail to judge yourself, God will take you home so you are no longer an embarrassment to Him.