It has always been my belief that everyone will be saved. I had this problem: when salvation arrived through Christ, what of those previously condemned? It seems to me Christ was looking for the salvation of all men. Surely he has the power to retrieve those who previously existed from hell after they have spent their term there, and would use this power. But religion speaks of "eternal damnation". Is this not something Christ would bring to an end, just as he came to redeem those who would at the time be believers?
The only men sent to hell are the ones dressed for war on the day the 7th trump sounds. Before then anybody who dies experiences the same thing , repented and un-repented alike.
Ec:3:20:
All go unto one place;
all are of the dust,
and all turn to dust again.
Ec:12:7:
Then shall the dust return to the earth as it was:
and the spirit shall return unto God who gave it.
Ge:2:7:
And the LORD God formed man of the dust of the ground,
and breathed into his nostrils the breath of life;
and man became a living soul.
The ones sent to hell for the 1,000 years are the same ones under punishment in Isa"65 and they are released and go onto be the ones building houses in the new earth verses of that chapter. The 'servants' in that chapter tale up residence inside New Jerusalem rather than outside it's walls.
The verses that answer the question about the same sparrows being alive in the new earth is a bit long but it does answer the question fully.