I believe that many Christians will lose some rewards, but they do not lose the Kingdom. There will be a great time of regret and remorse. the Bema Seat will not be a continual happy time like some graduation ceremony, although there will be much joy there as well---especially when it is over! We will cast our crowns before Him, and He will dry our eyes!
A conditiion for enterning the kingdom is for us to humble ourselves as a little child. " ... Truly I say to you, Unless you turn and become like little children, you shall by no menas enter into the kingdom of the heavens." ( See Matt. 18:1-3)
So we surely need to turn to Christ for He alone has the humility and meekness needed for the kingdom of the heavens.
But you have to admit that here Jesus is speaking about entering or not entering. So the realm of the kingdom of the heavens in the millennium is something the disciples will enter or not enter. That is how I read it.
We have to be as a little humble child to enter. Then we have to continue in the same manner. The way we enter is the way we must continue - as a little child. We must still be facing the same direction.
To enter we must turn to become as a little child. Then to be greatest we must still be as a little child. Then we must continue on as a little child in childlike humbleness.
May the Lord have mercy on us to be so.